diff --git a/src/c_gen_be.c b/src/c_gen_be.c
index 644f356700..86cd0fc9ff 100644
--- a/src/c_gen_be.c
+++ b/src/c_gen_be.c
@@ -10851,12 +10851,19 @@ if this routine has a body (dump nothing if it has no body).
   a_boolean       is_marked_weak = FALSE;
   a_boolean       thread_local_init_case = FALSE;
   a_boolean       for_inlining_only;
+  a_boolean       inline_only_defn = FALSE;
+  a_boolean       need_gnu_inline_attr = FALSE;
 
   if (c99_mode && rout->definition_for_inlining_only &&
-      !gcc_version_is(< 50000)) {
+      !gcc_version_is(< 50000)
+#if GNU_EXTENSIONS_ALLOWED
+      && !rout->gnu_c89_inline
+#endif /* GNU_EXTENSIONS_ALLOWED */
+                              ) {
     /* This is a C99 "inline definition", so we must suppress the "extern"
        keyword to avoid turning it into an external definition.  (gcc did
-       not support C99 inline semantics until version 5.1.0.) */
+       not support C99 inline semantics until version 5.1.0.  A routine with
+       the gnu_inline attribute follows the GNU C89 rules instead.) */
     for_inlining_only = TRUE;
   } else {
     for_inlining_only = FALSE;
@@ -10881,8 +10888,29 @@ if this routine has a body (dump nothing if it has no body).
          provided only for the purpose of inlining -- "extern inline".
          Put out the definition in that case. */
       has_defn = TRUE;
+      inline_only_defn = TRUE;
       if (!for_inlining_only) {
         storage_class = (a_storage_class)sc_extern;
+        /* "extern inline" is a definition only for inlining under the GNU
+           C89 rules, but an external definition under the C99 rules (used
+           by gcc in C99 modes since 4.3, and by default since 5.1), so
+           request the former with the gnu_inline attribute.  As in
+           form_routine_attributes, omit it for gcc before 4.2, which does
+           not recognize it but always follows the GNU C89 rules. */
+        need_gnu_inline_attr = TRUE;
+#if GCC_IS_GENERATED_CODE_TARGET
+        if (gcc_is_generated_code_target &&
+            gnu_target_version_number < 40200) {
+          need_gnu_inline_attr = FALSE;
+        }  /* if */
+#endif /* GCC_IS_GENERATED_CODE_TARGET */
+#if GNU_EXTENSIONS_ALLOWED
+        if (rout->gnu_c89_inline) {
+          /* form_routine_attributes already puts out the gnu_inline
+             attribute for this routine. */
+          need_gnu_inline_attr = FALSE;
+        }  /* if */
+#endif /* GNU_EXTENSIONS_ALLOWED */
       }  /* if */
     }  /* if */
   }  /* if */
@@ -11145,13 +11173,17 @@ if this routine has a body (dump nothing if it has no body).
       /* gcc will be used to compile this generated code, so we know how to
          indicate an inline function. */
       /* gcc ignores __inline__ on functions with ellipses, so don't
-         mark such functions as inline.  Recent versions of gcc issue an
-         error for a function marked both inline and weak, so don't mark a
-         weak function as inline, either. */
-      if (!f_skip_typerefs(rout->type)->variant.routine.extra_info->
-                                                                has_ellipsis &&
+         mark such functions as inline, except for a definition only for
+         inlining, which would otherwise be an external definition.  Recent
+         versions of gcc issue an error for a function marked both inline and
+         weak, so don't mark a weak function as inline, either. */
+      if ((!rout_type_supp(f_skip_typerefs(rout->type))->has_ellipsis ||
+           inline_only_defn) &&
           !is_marked_weak) {
         write_tok_str("__inline__ ");
+        if (need_gnu_inline_attr) {
+          write_tok_str("__attribute__((__gnu_inline__)) ");
+        }  /* if */
       }  /* if */
     }  /* if */
 #if GNU_EXTENSIONS_ALLOWED && !LOWER_IFUNC
diff --git a/src/pending_changes/gh-252-extern-inline-definitions.txt b/src/pending_changes/gh-252-extern-inline-definitions.txt
new file mode 100644
index 0000000000..b639983f37
--- /dev/null
+++ b/src/pending_changes/gh-252-extern-inline-definitions.txt
@@ -0,0 +1,38 @@
+[GH #252]
+C-generating back end: inline-only definitions emitted as external ones
+
+When an inline function definition was to be used only for inlining (for
+example, a member of a class template specialization that is the subject of
+an explicit instantiation declaration), the C-generating back end emitted it
+as an "extern __inline__" definition for GCC and Clang.  That form is a
+definition only for inlining under the GNU C89 rules, but an external
+definition under the C99 rules that GCC uses by default since version 5.
+Every object file that used such a function then contained an external
+definition of it, and linking two such object files failed.  For example,
+with --c++17:
+
+  // a.h
+  template <class T> struct A {
+    int f() { return 1; }
+  };
+  extern template struct A<int>;
+
+  // a.cpp
+  #include "a.h"
+  int g1() { return A<int>().f(); }
+
+  // b.cpp
+  #include "a.h"
+  int g2() { return A<int>().f(); }  // Linking with a.cpp previously failed.
+
+  // c.cpp
+  #include "a.h"
+  template struct A<int>;
+
+The same problem affected GNU C89 "extern inline" functions, functions with
+the gnu_inline attribute in C99 and later C modes (which lost the "extern"
+keyword), and such definitions of functions with an ellipsis (which were not
+marked inline).  This is now fixed: The C-generating back end now adds the
+__gnu_inline__ attribute to "extern __inline__" definitions, keeps "extern"
+for functions with the gnu_inline attribute, and marks a definition only for
+inlining as inline even when the function has an ellipsis.
diff --git a/tests/expectations/edg_x86_64/imported.log b/tests/expectations/edg_x86_64/imported.log
index ada16fd747..322752f038 100644
--- a/tests/expectations/edg_x86_64/imported.log
+++ b/tests/expectations/edg_x86_64/imported.log
@@ -4211,7 +4211,6 @@ gnu/c/torture/pr68661-1a.sft.c:s:-DTEST_NUMBER=1:SKIPPED:
 gnu/c/torture/pr68661-1b.sft.c:s:-DTEST_NUMBER=1:SKIPPED:
 gnu/c/torture/pr69242.sft.c:fp:-DTEST_NUMBER=1 -w:FAIL:
 gnu/c/torture/pr69886.sft.c:s:-DTEST_NUMBER=1 -w:SKIPPED:
-gnu/c/torture/pr70123.sft.c:rp:-DTEST_NUMBER=1:BADC(COMPILE):
 gnu/c/torture/pr70457.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr70985.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr71594.sft.c:s:-DTEST_NUMBER=1:SKIPPED:
diff --git a/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.1.txt b/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.1.txt
index 6122b6ca2b..6b1a64e524 100644
--- a/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.1.txt
+++ b/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.1.txt
@@ -59,8 +59,3 @@ eccp -DTEST_NUMBER=1 --gnu_version=999999 -e 200 --no_wrap --no_wrap_diagnostics
   __attribute__ ((noinline, noclone)) int
                             ^
 
-eccp: diagnostics generated from compilation of Test_name.int.c:
-Test_name.c: In function 'baz':
-Test_name.c:15:8: error: invalid use of '__builtin_va_arg_pack ()'
-eccp: end of diagnostics from compilation of Test_name.int.c
-eccp: gcc compilation of Test_name.int.c returned an exit status of 1
diff --git a/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.2.txt b/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_32_cp.1.1.txt b/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_32_cp.1.1.txt
index 745f05b3b6..531b329c84 100644
--- a/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_32_cp.1.1.txt
+++ b/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_32_cp.1.1.txt
@@ -1,6 +1 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -e 200 --no_wrap --no_wrap_diagnostics --gcc Test_name.c
-eccp: diagnostics generated from compilation of Test_name.int.c:
-Test_name.c: In function 'baz':
-Test_name.c:15:8: error: invalid use of '__builtin_va_arg_pack ()'
-eccp: end of diagnostics from compilation of Test_name.int.c
-eccp: gcc compilation of Test_name.int.c returned an exit status of 1
diff --git a/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_64_cp.1.1.txt b/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_64_cp.1.1.txt
index 745f05b3b6..531b329c84 100644
--- a/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_64_cp.1.1.txt
+++ b/tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_64_cp.1.1.txt
@@ -1,6 +1 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -e 200 --no_wrap --no_wrap_diagnostics --gcc Test_name.c
-eccp: diagnostics generated from compilation of Test_name.int.c:
-Test_name.c: In function 'baz':
-Test_name.c:15:8: error: invalid use of '__builtin_va_arg_pack ()'
-eccp: end of diagnostics from compilation of Test_name.int.c
-eccp: gcc compilation of Test_name.int.c returned an exit status of 1
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/default.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/default.1.1.txt
index c6cecbacaa..7319dec802 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/default.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/default.1.1.txt
@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:108: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:114: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:103:
 ./ext/va-arg-pack-1.C:127:108: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32.1.1.txt
index 0d28c7d687..a006454d35 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32.1.1.txt
@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:93: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:99: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:88:
 ./ext/va-arg-pack-1.C:127:93: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32_cp.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32_cp.1.1.txt
index cacadf2663..4803c8057f 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32_cp.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32_cp.1.1.txt
@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:92: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:98: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:88:
 ./ext/va-arg-pack-1.C:127:92: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_64_cp.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_64_cp.1.1.txt
index f4bcf016bc..25e22e7512 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_64_cp.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_64_cp.1.1.txt
@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:107: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:113: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:103:
 ./ext/va-arg-pack-1.C:127:107: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/default.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/default.1.1.txt
index 0185978c0f..a23e9136b3 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/default.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/default.1.1.txt
@@ -1,9 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-len-1.C: In function '_Z6myopenPKciz':
-./ext/va-arg-pack-len-1.C:81:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:94:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:97:113: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z6myopenPKciz',
     inlined from 'main' at ./ext/va-arg-pack-len-1.C:106:5:
 ./ext/va-arg-pack-len-1.C:97:113: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32.1.1.txt
index 44837a133e..a2db210ce2 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32.1.1.txt
@@ -1,9 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-len-1.C: In function '_Z6myopenPKciz':
-./ext/va-arg-pack-len-1.C:81:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:94:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:97:98: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z6myopenPKciz',
     inlined from 'main' at ./ext/va-arg-pack-len-1.C:106:5:
 ./ext/va-arg-pack-len-1.C:97:98: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32_cp.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32_cp.1.1.txt
index 2041861774..6eb429c218 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32_cp.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_32_cp.1.1.txt
@@ -1,9 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-len-1.C: In function '_Z6myopenPKciz':
-./ext/va-arg-pack-len-1.C:81:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:94:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:97:96: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z6myopenPKciz',
     inlined from 'main' at ./ext/va-arg-pack-len-1.C:106:5:
 ./ext/va-arg-pack-len-1.C:97:96: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_64_cp.1.1.txt b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_64_cp.1.1.txt
index dd35fd4688..ac46c2dd13 100644
--- a/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_64_cp.1.1.txt
+++ b/tests/tests/imported/gnu/cpp/ext/.va-arg-pack-len-1.rto/edg_x86_64_cp.1.1.txt
@@ -1,9 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-len-1.C: In function '_Z6myopenPKciz':
-./ext/va-arg-pack-len-1.C:81:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:94:6: error: invalid use of '__builtin_va_arg_pack_len ()'
-./ext/va-arg-pack-len-1.C:97:111: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z6myopenPKciz',
     inlined from 'main' at ./ext/va-arg-pack-len-1.C:106:5:
 ./ext/va-arg-pack-len-1.C:97:111: error: invalid use of '__builtin_va_arg_pack ()'
diff --git a/tests/tests/regressions/gh-252-c/.test.rto/default.1.1.txt b/tests/tests/regressions/gh-252-c/.test.rto/default.1.1.txt
new file mode 100644
index 0000000000..dd835ceabf
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/.test.rto/default.1.1.txt
@@ -0,0 +1,4 @@
+eccp -DTEST_NUMBER=1 --c11 Test_name.c use.c def.c
+Test_name.c:
+use.c:
+def.c:
diff --git a/tests/tests/regressions/gh-252-c/.test.rto/default.1.2.txt b/tests/tests/regressions/gh-252-c/.test.rto/default.1.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/.test.rto/default.1.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252-c/.test.rto/default.2.1.txt b/tests/tests/regressions/gh-252-c/.test.rto/default.2.1.txt
new file mode 100644
index 0000000000..1d10c3be1d
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/.test.rto/default.2.1.txt
@@ -0,0 +1,4 @@
+eccp -DTEST_NUMBER=2 --c11 --gnu=150100 Test_name.c use.c def.c
+Test_name.c:
+use.c:
+def.c:
diff --git a/tests/tests/regressions/gh-252-c/.test.rto/default.2.2.txt b/tests/tests/regressions/gh-252-c/.test.rto/default.2.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/.test.rto/default.2.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252-c/.test.rto/default.3.1.txt b/tests/tests/regressions/gh-252-c/.test.rto/default.3.1.txt
new file mode 100644
index 0000000000..d63b3e6e68
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/.test.rto/default.3.1.txt
@@ -0,0 +1,4 @@
+eccp -DTEST_NUMBER=3 --c --gnu=40200 Test_name.c use.c def.c
+Test_name.c:
+use.c:
+def.c:
diff --git a/tests/tests/regressions/gh-252-c/.test.rto/default.3.2.txt b/tests/tests/regressions/gh-252-c/.test.rto/default.3.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/.test.rto/default.3.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252-c/def.c b/tests/tests/regressions/gh-252-c/def.c
new file mode 100644
index 0000000000..b4d07d382e
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/def.c
@@ -0,0 +1,3 @@
+int h(void) { return 1; }
+int v(int n, ...) { return n; }
+int k(void) { return 1; }
diff --git a/tests/tests/regressions/gh-252-c/inl.h b/tests/tests/regressions/gh-252-c/inl.h
new file mode 100644
index 0000000000..a4885b4258
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/inl.h
@@ -0,0 +1,13 @@
+/* Definitions only for inlining. */
+#if __GNUC_GNU_INLINE__
+#define INLINE_ONLY extern inline
+#else
+#define INLINE_ONLY inline
+#endif
+INLINE_ONLY int h(void) { return 1; }
+INLINE_ONLY int v(int n, ...) { return n; }
+#ifdef __GNUC__
+extern inline __attribute__((gnu_inline)) int k(void) { return 1; }
+#else
+INLINE_ONLY int k(void) { return 1; }
+#endif
diff --git a/tests/tests/regressions/gh-252-c/test.mft.c b/tests/tests/regressions/gh-252-c/test.mft.c
new file mode 100644
index 0000000000..fa2df78bf2
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/test.mft.c
@@ -0,0 +1,11 @@
+//type:rp
+//options:--c11:--c11 --gnu=150100:--c --gnu=40200
+//source_files:inl.h use.c def.c
+/* h, v, and k are used here and in use.c, but only def.c may define them.
+   Each object used to contain an external definition of v, of h (with the
+   GNU C89 inline rules), or of k (with the C99 inline rules). */
+#include "inl.h"
+int use(void);
+int main(void) {
+  return (h() == 1 && v(1, 2) == 1 && k() == 1 && use() == 3) ? 0 : 1;
+}
diff --git a/tests/tests/regressions/gh-252-c/use.c b/tests/tests/regressions/gh-252-c/use.c
new file mode 100644
index 0000000000..821a2cd8fd
--- /dev/null
+++ b/tests/tests/regressions/gh-252-c/use.c
@@ -0,0 +1,2 @@
+#include "inl.h"
+int use(void) { return h() + v(1, 3) + k(); }
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.1.1.txt b/tests/tests/regressions/gh-252/.test.rto/default.1.1.txt
new file mode 100644
index 0000000000..9fddda4ac1
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.1.1.txt
@@ -0,0 +1,7 @@
+./check_defs -DTEST_NUMBER=1 --c++17 Test_name.c use.C inst.C
+Test_name.c:
+use.C:
+inst.C:
+Test_name.o:
+use.o:
+inst.o: _ZN1AIiE1fEv _ZN1AIiE1gEiz
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.1.2.txt b/tests/tests/regressions/gh-252/.test.rto/default.1.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.1.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.2.1.txt b/tests/tests/regressions/gh-252/.test.rto/default.2.1.txt
new file mode 100644
index 0000000000..1371461338
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.2.1.txt
@@ -0,0 +1,7 @@
+./check_defs -DTEST_NUMBER=2 --c++17 --g++ Test_name.c use.C inst.C
+Test_name.c:
+use.C:
+inst.C:
+Test_name.o:
+use.o:
+inst.o: _ZN1AIiE1fEv _ZN1AIiE1gEiz
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.2.2.txt b/tests/tests/regressions/gh-252/.test.rto/default.2.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.2.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.3.1.txt b/tests/tests/regressions/gh-252/.test.rto/default.3.1.txt
new file mode 100644
index 0000000000..38e27fcbb3
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.3.1.txt
@@ -0,0 +1,7 @@
+./check_defs -DTEST_NUMBER=3 --c++17 --g++ -tused Test_name.c use.C inst.C
+Test_name.c:
+use.C:
+inst.C:
+Test_name.o:
+use.o:
+inst.o: _ZN1AIiE1fEv _ZN1AIiE1gEiz
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.3.2.txt b/tests/tests/regressions/gh-252/.test.rto/default.3.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.3.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.4.1.txt b/tests/tests/regressions/gh-252/.test.rto/default.4.1.txt
new file mode 100644
index 0000000000..3f77797318
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.4.1.txt
@@ -0,0 +1,7 @@
+./check_defs -DTEST_NUMBER=4 --c++17 --clang Test_name.c use.C inst.C
+Test_name.c:
+use.C:
+inst.C:
+Test_name.o:
+use.o:
+inst.o: _ZN1AIiE1fEv _ZN1AIiE1gEiz
diff --git a/tests/tests/regressions/gh-252/.test.rto/default.4.2.txt b/tests/tests/regressions/gh-252/.test.rto/default.4.2.txt
new file mode 100644
index 0000000000..ff2642c6d5
--- /dev/null
+++ b/tests/tests/regressions/gh-252/.test.rto/default.4.2.txt
@@ -0,0 +1 @@
+./a.out
diff --git a/tests/tests/regressions/gh-252/a.h b/tests/tests/regressions/gh-252/a.h
new file mode 100644
index 0000000000..297a0271c8
--- /dev/null
+++ b/tests/tests/regressions/gh-252/a.h
@@ -0,0 +1,5 @@
+template <class T> struct A {
+  int f() { return 1; }
+  int g(int n, ...) { return n; }
+};
+extern template struct A<int>;
diff --git a/tests/tests/regressions/gh-252/check_defs b/tests/tests/regressions/gh-252/check_defs
new file mode 100755
index 0000000000..529e7bcbe9
--- /dev/null
+++ b/tests/tests/regressions/gh-252/check_defs
@@ -0,0 +1,31 @@
+#!/bin/bash
+# Compile each source file to an object file, check that only inst.o (the
+# explicit instantiation) defines A<int>::f and A<int>::g, and then link the
+# object files.
+opts=
+objs=
+for arg in "$@"; do
+  case $arg in
+    *.c | *.C) objs="$objs ${arg%.*}.o" ;;
+    *) opts="$opts $arg" ;;
+  esac
+done
+eccp -c "$@" || exit $?
+status=0
+for obj in $objs; do
+  defs=`nm -g --defined-only $obj | grep -o '_ZN1AIiE1[fg]E[a-z]*' | sort`
+  defs=`echo $defs`
+  echo $obj: $defs
+  expected=
+  if [ $obj = inst.o ]; then
+    expected="_ZN1AIiE1fEv _ZN1AIiE1gEiz"
+  fi
+  if [ "$defs" != "$expected" ]; then
+    echo "FAIL: Expected '$expected'."
+    status=1
+  fi
+done
+if [ $status -ne 0 ]; then
+  exit $status
+fi
+exec eccp $opts $objs
diff --git a/tests/tests/regressions/gh-252/inst.C b/tests/tests/regressions/gh-252/inst.C
new file mode 100644
index 0000000000..fb8d2dec70
--- /dev/null
+++ b/tests/tests/regressions/gh-252/inst.C
@@ -0,0 +1,2 @@
+#include "a.h"
+template struct A<int>;
diff --git a/tests/tests/regressions/gh-252/test.mft.cpp b/tests/tests/regressions/gh-252/test.mft.cpp
new file mode 100644
index 0000000000..66e8cc51f5
--- /dev/null
+++ b/tests/tests/regressions/gh-252/test.mft.cpp
@@ -0,0 +1,11 @@
+//type:rp
+//options:--c++17:--c++17 --g++:--c++17 --g++ -tused:--c++17 --clang
+//source_files:a.h use.C inst.C
+//script:./check_defs
+// The members of A<int> are used here and in use.C, but only inst.C may
+// define them; each object used to contain an external definition.
+#include "a.h"
+int use();
+int main() {
+  return (A<int>().f() == 1 && A<int>().g(1, 2) == 1 && use() == 2) ? 0 : 1;
+}
diff --git a/tests/tests/regressions/gh-252/use.C b/tests/tests/regressions/gh-252/use.C
new file mode 100644
index 0000000000..feeb2a7ab7
--- /dev/null
+++ b/tests/tests/regressions/gh-252/use.C
@@ -0,0 +1,2 @@
+#include "a.h"
+int use() { return A<int>().f() + A<int>().g(1, 3); }