diff --git a/src/profile-logic/profile-data.ts b/src/profile-logic/profile-data.ts
index 002ac3514d..baed4507e9 100644
--- a/src/profile-logic/profile-data.ts
+++ b/src/profile-logic/profile-data.ts
@@ -4660,6 +4660,35 @@ export function nudgeReturnAddresses(profile: Profile): Profile {
   return newProfile;
 }
 
+/**
+ * The source of a frame with an address, which is what can prove to the
+ * symbolication API's /source/v1 that the source belongs to the library. Null
+ * when the frame has no address or its func no source.
+ */
+function _getAddressProvenSource(
+  frameTable: RawFrameTable,
+  funcTable: RawFuncTable,
+  frameIndex: IndexIntoFrameTable
+): IndexIntoSourceTable | null {
+  if ((frameTable.flags[frameIndex] & FrameFlag.HasAddress) === 0) {
+    return null;
+  }
+  const funcIndex = frameTable.func[frameIndex];
+  if ((funcTable.flags[funcIndex] & FuncFlag.HasSource) === 0) {
+    return null;
+  }
+  return funcTable.source[funcIndex];
+}
+
+function _getAddressProofForFrame(
+  profile: Profile,
+  frameIndex: IndexIntoFrameTable
+): AddressProof {
+  const { frameTable } = profile.shared;
+  const { debugName, breakpadId } = profile.libs[frameTable.lib[frameIndex]];
+  return { debugName, breakpadId, address: frameTable.address[frameIndex] };
+}
+
 /**
  * Find the address and library (debugName, breakpadId) for any frame which
  * was symbolicated to the given filename.
@@ -4668,41 +4697,15 @@ export function findAddressProofForFile(
   profile: Profile,
   sourceIndex: IndexIntoSourceTable
 ): AddressProof | null {
-  const { libs } = profile;
   const { frameTable, funcTable } = profile.shared;
-  // Scan for the func manually rather than using `funcTable.source.indexOf`:
-  // the `source` column only carries a meaningful value for funcs which have
-  // the `HasSource` flag set, and holds an arbitrary value (usually zero) for
-  // all other funcs. An `indexOf` would happily match one of those.
-  let func = -1;
-  for (let i = 0; i < funcTable.length; i++) {
+  for (let frameIndex = 0; frameIndex < frameTable.length; frameIndex++) {
     if (
-      (funcTable.flags[i] & FuncFlag.HasSource) !== 0 &&
-      funcTable.source[i] === sourceIndex
+      _getAddressProvenSource(frameTable, funcTable, frameIndex) === sourceIndex
     ) {
-      func = i;
-      break;
+      return _getAddressProofForFrame(profile, frameIndex);
     }
   }
-  if (func === -1) {
-    return null;
-  }
-  const frame = frameTable.func.indexOf(func);
-  if (frame === -1) {
-    return null;
-  }
-  if ((frameTable.flags[frame] & FrameFlag.HasAddress) === 0) {
-    return null;
-  }
-  const address = frameTable.address[frame];
-  const libIndex = frameTable.lib[frame];
-  const lib = libs[libIndex];
-  const { debugName, breakpadId } = lib;
-  return {
-    debugName,
-    breakpadId,
-    address,
-  };
+  return null;
 }
 
 /**
diff --git a/src/test/unit/profile-data.test.ts b/src/test/unit/profile-data.test.ts
index 0e83649442..d8256f3af6 100644
--- a/src/test/unit/profile-data.test.ts
+++ b/src/test/unit/profile-data.test.ts
@@ -1546,6 +1546,25 @@ describe('findAddressProofForFile', function () {
     );
     expect(missingAddressProof).toBeNull();
   });
+
+  it('finds an address for a file whose first frame has none', function () {
+    const { profile } = getProfileFromTextSamples(`
+      A[lib:XUL][file:a.cpp]
+      B[lib:XUL][file:a.cpp][address:20]
+    `);
+    const stringTable = StringTable.withBackingArray(
+      profile.shared.stringArray
+    );
+    const sourceIndex = profile.shared.sources.filename.indexOf(
+      stringTable.indexForString('a.cpp')
+    );
+
+    expect(findAddressProofForFile(profile, sourceIndex)).toEqual({
+      debugName: 'XUL',
+      breakpadId: 'SOMETHING_FAKE',
+      address: 0x20,
+    });
+  });
 });
 
 describe('calculateFunctionSizeLowerBound', function () {