diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index ea4b233a6c573..ca09c3d79d941 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -5329,7 +5329,7 @@ llvm::Error ASTReader::ReadExtensionBlock(ModuleFile &F) {
     }
   }
 
-  return llvm::Error::success();
+  llvm_unreachable("ReadExtensionBlock should return from while loop");
 }
 
 void ASTReader::InitializeContext() {