diff --git a/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h b/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
--- a/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
+++ b/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
@@ -32,12 +32,14 @@
 struct PrebuiltModuleDep {
   std::string ModuleName;
   std::string PCMFile;
-  std::string ModuleMapFile;
+  Optional<std::string> ModuleMapFile;
 
   explicit PrebuiltModuleDep(const Module *M)
       : ModuleName(M->getTopLevelModuleName()),
         PCMFile(M->getASTFile()->getName()),
-        ModuleMapFile(M->PresumedModuleMapFile) {}
+        ModuleMapFile(M->PresumedModuleMapFile.empty()
+                          ? None
+                          : Optional<std::string>(M->PresumedModuleMapFile)) {}
 };
 
 /// This is used to identify a specific module.
diff --git a/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp b/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp
--- a/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp
+++ b/clang/lib/Tooling/DependencyScanning/DependencyScanningTool.cpp
@@ -39,7 +39,8 @@
 
   for (const PrebuiltModuleDep &PMD : PrebuiltModuleDeps) {
     Args.push_back("-fmodule-file=" + PMD.ModuleName + "=" + PMD.PCMFile);
-    Args.push_back("-fmodule-map-file=" + PMD.ModuleMapFile);
+    if (PMD.ModuleMapFile)
+      Args.push_back("-fmodule-map-file=" + *PMD.ModuleMapFile);
   }
 
   return Args;
diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -35,7 +35,9 @@
   // Report the prebuilt modules this module uses.
   for (const auto &PrebuiltModule : Deps.PrebuiltModuleDeps) {
     CI.getFrontendOpts().ModuleFiles.push_back(PrebuiltModule.PCMFile);
-    CI.getFrontendOpts().ModuleMapFiles.push_back(PrebuiltModule.ModuleMapFile);
+    if (PrebuiltModule.ModuleMapFile)
+      CI.getFrontendOpts().ModuleMapFiles.push_back(
+          *PrebuiltModule.ModuleMapFile);
   }
 
   CI.getPreprocessorOpts().ImplicitPCHInclude.clear();