Index: clang/include/clang/CodeGen/BackendUtil.h
===================================================================
--- clang/include/clang/CodeGen/BackendUtil.h
+++ clang/include/clang/CodeGen/BackendUtil.h
@@ -49,6 +49,8 @@
 
   llvm::Expected<llvm::BitcodeModule>
   FindThinLTOModule(llvm::MemoryBufferRef MBRef);
+  llvm::BitcodeModule *
+  FindThinLTOModule(llvm::MutableArrayRef<llvm::BitcodeModule> BMs);
 }
 
 #endif
Index: clang/lib/CodeGen/BackendUtil.cpp
===================================================================
--- clang/lib/CodeGen/BackendUtil.cpp
+++ clang/lib/CodeGen/BackendUtil.cpp
@@ -1025,16 +1025,22 @@
 
   // The bitcode file may contain multiple modules, we want the one that is
   // marked as being the ThinLTO module.
-  for (BitcodeModule &BM : *BMsOrErr) {
-    Expected<BitcodeLTOInfo> LTOInfo = BM.getLTOInfo();
-    if (LTOInfo && LTOInfo->IsThinLTO)
-      return BM;
-  }
+  if (const BitcodeModule *Bm = FindThinLTOModule(*BMsOrErr))
+    return *Bm;
 
   return make_error<StringError>("Could not find module summary",
                                  inconvertibleErrorCode());
 }
 
+BitcodeModule *clang::FindThinLTOModule(MutableArrayRef<BitcodeModule> BMs) {
+  for (BitcodeModule &BM : BMs) {
+    Expected<BitcodeLTOInfo> LTOInfo = BM.getLTOInfo();
+    if (LTOInfo && LTOInfo->IsThinLTO)
+      return &BM;
+  }
+  return nullptr;
+}
+
 static void runThinLTOBackend(ModuleSummaryIndex *CombinedIndex, Module *M,
                               const HeaderSearchOptions &HeaderOpts,
                               const CodeGenOptions &CGOpts,
Index: clang/lib/CodeGen/CodeGenAction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenAction.cpp
+++ clang/lib/CodeGen/CodeGenAction.cpp
@@ -947,12 +947,18 @@
       return {};
     };
 
-    Expected<llvm::BitcodeModule> BMOrErr = FindThinLTOModule(MBRef);
-    if (!BMOrErr)
-      return DiagErrors(BMOrErr.takeError());
-
+    Expected<std::vector<BitcodeModule>> BMsOrErr = getBitcodeModuleList(MBRef);
+    if (!BMsOrErr)
+      return DiagErrors(BMsOrErr.takeError());
+    BitcodeModule *Bm = FindThinLTOModule(*BMsOrErr);
+    // We have nothing to do if the file contains no ThinLTO module. This is
+    // possible if ThinLTO compilation was not able to split module. Content of
+    // the file was already processed by indexing and will be passed to the
+    // linker using merged object file.
+    if (!Bm)
+      return {};
     Expected<std::unique_ptr<llvm::Module>> MOrErr =
-        BMOrErr->parseModule(*VMContext);
+        Bm->parseModule(*VMContext);
     if (!MOrErr)
       return DiagErrors(MOrErr.takeError());
     return std::move(*MOrErr);
Index: clang/test/CodeGen/thinlto_backend.ll
===================================================================
--- clang/test/CodeGen/thinlto_backend.ll
+++ clang/test/CodeGen/thinlto_backend.ll
@@ -20,6 +20,11 @@
 ; CHECK-OBJ-IGNORE-EMPTY: T f1
 ; CHECK-OBJ-IGNORE-EMPTY: U f2
 
+; Ensure we don't fail with index and non-ThinLTO object file, and run
+; non-ThinLTO compilation which
+; RUN: opt -o %t5.o %s
+; RUN: %clang -target x86_64-unknown-linux-gnu -O2 -o %t4.o -x ir %t5.o -c -fthinlto-index=%t.thinlto.bc
+
 ; Ensure f2 was imported
 ; RUN: %clang -target x86_64-unknown-linux-gnu -O2 -o %t3.o -x ir %t1.o -c -fthinlto-index=%t.thinlto.bc
 ; RUN: llvm-nm %t3.o | FileCheck --check-prefix=CHECK-OBJ %s