diff --git a/include/clang/Frontend/ASTUnit.h b/include/clang/Frontend/ASTUnit.h
index 7d9d121..d326a53 100644
--- a/include/clang/Frontend/ASTUnit.h
+++ b/include/clang/Frontend/ASTUnit.h
@@ -827,6 +827,8 @@
   ///
   /// \param ResourceFilesPath - The path to the compiler resource files.
   ///
+  /// \param ModuleFormat - If provided, uses the specific module format.
+  ///
   /// \param ErrAST - If non-null and parsing failed without any AST to return
   /// (e.g. because the PCH could not be loaded), this accepts the ASTUnit
   /// mainly to allow the caller to see the diagnostics.
@@ -845,6 +847,7 @@
       bool IncludeBriefCommentsInCodeCompletion = false,
       bool AllowPCHWithCompilerErrors = false, bool SkipFunctionBodies = false,
       bool UserFilesAreVolatile = false, bool ForSerialization = false,
+      llvm::Optional<StringRef> ModuleFormat = llvm::None,
       std::unique_ptr<ASTUnit> *ErrAST = nullptr);
 
   /// \brief Reparse the source files using the same command-line options that
diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index 6b89447..0d5dd53 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -1934,6 +1934,7 @@
     bool CacheCodeCompletionResults, bool IncludeBriefCommentsInCodeCompletion,
     bool AllowPCHWithCompilerErrors, bool SkipFunctionBodies,
     bool UserFilesAreVolatile, bool ForSerialization,
+    llvm::Optional<StringRef> ModuleFormat,
     std::unique_ptr<ASTUnit> *ErrAST) {
   assert(Diags.get() && "no DiagnosticsEngine was provided");
 
@@ -1967,6 +1968,9 @@
 
   CI->getFrontendOpts().SkipFunctionBodies = SkipFunctionBodies;
 
+  if (ModuleFormat)
+    CI->getHeaderSearchOpts().ModuleFormat = ModuleFormat.getValue();
+
   // Create the AST unit.
   std::unique_ptr<ASTUnit> AST;
   AST.reset(new ASTUnit(false));
diff --git a/test/Index/annotate-module.m b/test/Index/annotate-module.m
index 456a192..24dce3f 100644
--- a/test/Index/annotate-module.m
+++ b/test/Index/annotate-module.m
@@ -6,6 +6,8 @@
 // RUN: rm -rf %t.cache
 // RUN: c-index-test -test-annotate-tokens=%s:2:1:5:1 %s -fmodules-cache-path=%t.cache -fmodules -F %S/../Modules/Inputs \
 // RUN:      | FileCheck %s
+// RUN: c-index-test -test-annotate-tokens=%s:2:1:5:1 %s -fmodules-cache-path=%t.cache -fmodules -gmodules -F %S/../Modules/Inputs \
+// RUN:      | FileCheck %s
 
 // CHECK:      Punctuation: "#" [2:1 - 2:2] inclusion directive=[[INC_DIR:DependsOnModule[/\\]DependsOnModule\.h \(.*/Modules/Inputs/DependsOnModule\.framework[/\\]Headers[/\\]DependsOnModule.h\)]]
 // CHECK-NEXT: Identifier: "include" [2:2 - 2:9] inclusion directive=[[INC_DIR]]
diff --git a/test/Index/complete-modules.m b/test/Index/complete-modules.m
index 175cf3d..21f0e4b 100644
--- a/test/Index/complete-modules.m
+++ b/test/Index/complete-modules.m
@@ -5,6 +5,7 @@
 
 // RUN: rm -rf %t
 // RUN: c-index-test -code-completion-at=%s:4:9 -fmodules-cache-path=%t -fmodules -F %S/Inputs/Frameworks -I %S/Inputs/Headers %s | FileCheck -check-prefix=CHECK-TOP-LEVEL %s
+// RUN: c-index-test -code-completion-at=%s:4:9 -fmodules-cache-path=%t -fmodules -gmodules -F %S/Inputs/Frameworks -I %S/Inputs/Headers %s | FileCheck -check-prefix=CHECK-TOP-LEVEL %s
 // CHECK-TOP-LEVEL: ModuleImport:{TypedText Framework} (50)
 // CHECK-TOP-LEVEL: ModuleImport:{TypedText LibA} (50)
 // CHECK-TOP-LEVEL: ModuleImport:{TypedText nested} (50)
diff --git a/test/Index/index-module.m b/test/Index/index-module.m
index a973e91..ff51259 100644
--- a/test/Index/index-module.m
+++ b/test/Index/index-module.m
@@ -6,6 +6,8 @@
 // RUN: rm -rf %t.cache
 // RUN: c-index-test -index-file %s -fmodules-cache-path=%t.cache -fmodules -F %S/../Modules/Inputs \
 // RUN:      -Xclang -fdisable-module-hash | FileCheck %s
+// RUN: c-index-test -index-file %s -fmodules-cache-path=%t.cache -fmodules -gmodules -F %S/../Modules/Inputs \
+// RUN:      -Xclang -fdisable-module-hash | FileCheck %s
 
 // CHECK-NOT: [indexDeclaration]
 // CHECK: [ppIncludedFile]: {{.*}}/Modules/Inputs/DependsOnModule.framework{{[/\\]}}Headers{{[/\\]}}DependsOnModule.h | name: "DependsOnModule/DependsOnModule.h" | hash loc: 2:1 | isImport: 0 | isAngled: 1 | isModule: 1
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index ac6f98d..5fa2566 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -3112,7 +3112,9 @@
       /*RemappedFilesKeepOriginalName=*/true, PrecompilePreamble, TUKind,
       CacheCodeCompletionResults, IncludeBriefCommentsInCodeCompletion,
       /*AllowPCHWithCompilerErrors=*/true, SkipFunctionBodies,
-      /*UserFilesAreVolatile=*/true, ForSerialization, &ErrUnit));
+      /*UserFilesAreVolatile=*/true, ForSerialization,
+      CXXIdx->getPCHContainerOperations()->getRawReader().getFormat(),
+      &ErrUnit));
 
   // Early failures in LoadFromCommandLine may return with ErrUnit unset.
   if (!Unit && !ErrUnit)
diff --git a/tools/libclang/Indexing.cpp b/tools/libclang/Indexing.cpp
index 8a04984..2b8daeb 100644
--- a/tools/libclang/Indexing.cpp
+++ b/tools/libclang/Indexing.cpp
@@ -566,6 +566,10 @@
   if (index_options & CXIndexOpt_SuppressWarnings)
     CInvok->getDiagnosticOpts().IgnoreWarnings = true;
 
+  // Make sure to use the raw module format.
+  CInvok->getHeaderSearchOpts().ModuleFormat =
+    CXXIdx->getPCHContainerOperations()->getRawReader().getFormat();
+
   ASTUnit *Unit = ASTUnit::create(CInvok.get(), Diags, CaptureDiagnostics,
                                   /*UserFilesAreVolatile=*/true);
   if (!Unit)