diff --git a/coverage/emitted-schema-known-failures.json b/coverage/emitted-schema-known-failures.json
index 02007b7..ee3e96a 100644
--- a/coverage/emitted-schema-known-failures.json
+++ b/coverage/emitted-schema-known-failures.json
@@ -1,10 +1,4 @@
 [
-  {
-    "id": "duplicate-rprchange-in-rpr",
-    "issue": "#451",
-    "match": "}rPrChange': This element is not expected.",
-    "reason": "comparison stacks duplicate w:rPrChange children in a single w:rPr; CT_RPr allows at most one"
-  },
   {
     "id": "duplicate-para-mark-ins",
     "issue": "#452",
diff --git a/packages/docx-core/src/baselines/atomizer/inPlaceModifier-wrappers.ts b/packages/docx-core/src/baselines/atomizer/inPlaceModifier-wrappers.ts
index 2c52a28..5c81380 100644
--- a/packages/docx-core/src/baselines/atomizer/inPlaceModifier-wrappers.ts
+++ b/packages/docx-core/src/baselines/atomizer/inPlaceModifier-wrappers.ts
@@ -421,6 +421,15 @@ export function addFormatChange(
     run.insertBefore(rPr, run.firstChild);
   }
 
+  // CT_RPr permits at most one w:rPrChange. Comparison can visit multiple
+  // format-changed atoms from the same split run, so keep the latest snapshot
+  // instead of stacking invalid siblings.
+  for (const child of childElements(rPr)) {
+    if (child.tagName === 'w:rPrChange') {
+      rPr.removeChild(child);
+    }
+  }
+
   // Create rPrChange
   const id = allocateRevisionId(state);
   const rPrChange = createEl('w:rPrChange', {
diff --git a/packages/docx-core/src/baselines/atomizer/inPlaceModifier.test.ts b/packages/docx-core/src/baselines/atomizer/inPlaceModifier.test.ts
index 6ca7fe3..0a8e598 100644
--- a/packages/docx-core/src/baselines/atomizer/inPlaceModifier.test.ts
+++ b/packages/docx-core/src/baselines/atomizer/inPlaceModifier.test.ts
@@ -1653,6 +1653,33 @@ describe('inPlaceModifier', () => {
         expect(childElements(innerRPr)).toHaveLength(3);
       });
     });
+
+    test('replaces an existing rPrChange instead of stacking duplicates', async ({ given, when, then }: AllureBddContext) => {
+      let r: Element;
+      let firstOldRPr: Element;
+      let secondOldRPr: Element;
+      let state: ReturnType<typeof createRevisionIdState>;
+
+      await given('a run whose formatting is visited twice by split format-changed atoms', () => {
+        r = el('w:r', {}, [el('w:rPr', {}, [el('w:b')]), el('w:t', {}, undefined, 'text')]);
+        firstOldRPr = el('w:rPr', {}, [el('w:i')]);
+        secondOldRPr = el('w:rPr', {}, [el('w:color', { 'w:val': 'FF0000' })]);
+        state = createRevisionIdState();
+      });
+
+      await when('addFormatChange is called twice for the same run', () => {
+        addFormatChange(r, firstOldRPr, author, dateStr, state);
+        addFormatChange(r, secondOldRPr, author, dateStr, state);
+      });
+
+      await then('the current rPr contains one replacement rPrChange snapshot', () => {
+        const rPr = childElements(r).find((c) => c.tagName === 'w:rPr')!;
+        const rPrChanges = childElements(rPr).filter((c) => c.tagName === 'w:rPrChange');
+        expect(rPrChanges).toHaveLength(1);
+        const innerRPr = childElements(rPrChanges[0]!).find((c) => c.tagName === 'w:rPr')!;
+        expect(childElements(innerRPr).map((c) => c.tagName)).toEqual(['w:color']);
+      });
+    });
   });
 
   // ── Branch coverage: preSplitMixedStatusRuns ──────────────────────