diff --git a/.changeset/unflatten-attributes-conflict.md b/.changeset/unflatten-attributes-conflict.md
new file mode 100644
index 00000000000..9df627f2630
--- /dev/null
+++ b/.changeset/unflatten-attributes-conflict.md
@@ -0,0 +1,5 @@
+---
+"@trigger.dev/core": patch
+---
+
+Fix `TypeError` in `unflattenAttributes` when the input attribute map contains conflicting dotted key paths (e.g. both `a.b` set to a scalar and `a.b.c` set to a value). The path-walk loop now applies last-write-wins when a prior key wrote a primitive, null, or array at an intermediate slot, matching the existing precedent in `AttributeFlattener.addAttribute`. Callers no longer crash when handed malformed external attribute inputs.
diff --git a/packages/core/src/v3/utils/flattenAttributes.ts b/packages/core/src/v3/utils/flattenAttributes.ts
index 83d1a14f2cd..1a4486a4e5d 100644
--- a/packages/core/src/v3/utils/flattenAttributes.ts
+++ b/packages/core/src/v3/utils/flattenAttributes.ts
@@ -312,10 +312,16 @@ export function unflattenAttributes(
       }
 
       if (typeof nextPart === "number") {
-        // Ensure we create an array for numeric indices
-        current[part] = Array.isArray(current[part]) ? current[part] : [];
-      } else if (current[part] === undefined) {
-        // Create an object for non-numeric paths
+        if (!Array.isArray(current[part])) {
+          current[part] = [];
+        }
+      } else if (
+        current[part] === null ||
+        typeof current[part] !== "object" ||
+        Array.isArray(current[part])
+      ) {
+        // Last-write-wins when a prior key wrote a primitive, null, or array
+        // at this slot — keeps unflatten total for conflicting OTLP inputs.
         current[part] = {};
       }
 
diff --git a/packages/core/test/flattenAttributes.test.ts b/packages/core/test/flattenAttributes.test.ts
index 28f137deaf9..3fd11fa5d04 100644
--- a/packages/core/test/flattenAttributes.test.ts
+++ b/packages/core/test/flattenAttributes.test.ts
@@ -667,4 +667,54 @@ describe("unflattenAttributes", () => {
     }
     expect(current).toBeUndefined();
   });
+
+  // Defends against external OTLP producers that emit both a leaf value and a
+  // nested path through the same prefix in one attribute map (e.g. AI SDK
+  // telemetry on certain models). The flattener can't produce these, but the
+  // unflattener used to crash with TypeError when it tried to descend into a
+  // primitive sibling.
+  it("does not throw when a scalar precedes a deeper path at the same prefix", () => {
+    expect(() =>
+      unflattenAttributes({ "a.b": "scalar", "a.b.c": "value" })
+    ).not.toThrow();
+    expect(unflattenAttributes({ "a.b": "scalar", "a.b.c": "value" })).toEqual({
+      a: { b: { c: "value" } },
+    });
+  });
+
+  it("does not throw when a deeper path precedes a scalar at the same prefix", () => {
+    expect(() =>
+      unflattenAttributes({ "a.b.c": "value", "a.b": "scalar" })
+    ).not.toThrow();
+    expect(unflattenAttributes({ "a.b.c": "value", "a.b": "scalar" })).toEqual({
+      a: { b: "scalar" },
+    });
+  });
+
+  it("treats an intermediate null sentinel as overwritable when a deeper path follows", () => {
+    expect(() =>
+      unflattenAttributes({ "a.b": "$@null((", "a.b.c": "value" })
+    ).not.toThrow();
+    expect(unflattenAttributes({ "a.b": "$@null((", "a.b.c": "value" })).toEqual({
+      a: { b: { c: "value" } },
+    });
+  });
+
+  it("does not throw when a scalar prefix conflicts with a numeric-index path", () => {
+    expect(() =>
+      unflattenAttributes({ "a.b": "scalar", "a.b.[0]": "indexed" })
+    ).not.toThrow();
+    expect(unflattenAttributes({ "a.b": "scalar", "a.b.[0]": "indexed" })).toEqual({
+      a: { b: ["indexed"] },
+    });
+  });
+
+  it("converts an existing object slot to an array when a numeric-index path follows", () => {
+    expect(() =>
+      unflattenAttributes({ "a.b.c": "value", "a.b.[0]": "indexed" })
+    ).not.toThrow();
+    expect(unflattenAttributes({ "a.b.c": "value", "a.b.[0]": "indexed" })).toEqual({
+      a: { b: ["indexed"] },
+    });
+  });
 });