diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1282,7 +1282,11 @@
     if (auto *AdditionalModMaps =
             Map.getAdditionalModuleMapFiles(WritingModule)) {
       Record.push_back(AdditionalModMaps->size());
-      for (const FileEntry *F : *AdditionalModMaps)
+      SmallVector<const FileEntry *, 1> ModMaps(AdditionalModMaps->begin(), AdditionalModMaps->end());
+      llvm::sort(ModMaps, [](const FileEntry *A, const FileEntry *B) {
+        return A->getName() < B->getName();
+      });
+      for (const FileEntry *F : ModMaps)
         AddPath(F->getName(), Record);
     } else {
       Record.push_back(0);