diff --git a/src/javascript/sourceMaps/SourceMapFormat.ts b/src/javascript/sourceMaps/SourceMapFormat.ts
index bebde09738..838c1082df 100644
--- a/src/javascript/sourceMaps/SourceMapFormat.ts
+++ b/src/javascript/sourceMaps/SourceMapFormat.ts
@@ -355,7 +355,10 @@ export const inspectSourceMapValue = (
     }
     const leaf = inspectLeaf(node, budget, options);
     leaves.push({ map: leaf, offset: node.offset, stop: node.stop });
-    if (options.profile !== "browser-collection")
+    if (options.profile !== "browser-collection") {
+      const ignoredSources = new Set(
+        leaf.ignoreList ?? leaf.x_google_ignoreList ?? [],
+      );
       for (const [sourceIndex, source] of leaf.sources.entries())
         declarations.push({
           sectionPath: node.path,
@@ -363,10 +366,9 @@ export const inspectSourceMapValue = (
           source,
           root: leaf.sourceRoot ?? null,
           content: leaf.sourcesContent?.[sourceIndex] ?? null,
-          ignored: (leaf.ignoreList ?? leaf.x_google_ignoreList ?? []).includes(
-            sourceIndex,
-          ),
+          ignored: ignoredSources.has(sourceIndex),
         });
+    }
   }
   return {
     format: root.sections === undefined ? "regular" : "indexed",
diff --git a/src/javascript/sourceMaps/TraceSourceMap.test.ts b/src/javascript/sourceMaps/TraceSourceMap.test.ts
index 0f3c6abdf0..ddb70b9fa4 100644
--- a/src/javascript/sourceMaps/TraceSourceMap.test.ts
+++ b/src/javascript/sourceMaps/TraceSourceMap.test.ts
@@ -29,6 +29,47 @@ it("traces BOM-prefixed maps with a source-map transport prefix ending in CR", (
   });
 });
 
+it("keeps ignore-list precedence and section-local indexes for duplicate sources", () => {
+  const map = {
+    version: 3,
+    sections: [
+      {
+        offset: { line: 0, column: 0 },
+        map: {
+          ...leaf,
+          sources: ["same.ts", "same.ts"],
+          sourcesContent: ["first", "second"],
+          mappings: "AAAA,ACAA",
+          ignoreList: [1, 1],
+          x_google_ignoreList: [0],
+        },
+      },
+      {
+        offset: { line: 1, column: 0 },
+        map: { ...leaf, x_google_ignoreList: [0] },
+      },
+      {
+        offset: { line: 2, column: 0 },
+        map: { ...leaf, ignoreList: [], x_google_ignoreList: [0] },
+      },
+    ],
+  };
+  expect(trace(map).matches).toMatchObject([
+    { source_index: 0, ignored: false, content: { text: "first" } },
+    { source_index: 1, ignored: true, content: { text: "second" } },
+  ]);
+  expect(trace(map, { line: 2, column: 0 }).matches[0]).toMatchObject({
+    section_path: [1],
+    source_index: 0,
+    ignored: true,
+  });
+  expect(trace(map, { line: 3, column: 0 }).matches[0]).toMatchObject({
+    section_path: [2],
+    source_index: 0,
+    ignored: false,
+  });
+});
+
 describe("upstream source-map point evidence", () => {
   it("preserves every duplicate-column/source-URL candidate and its own embedded bytes", () => {
     const report = trace({