diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 5aa0011d80efb..84bee2ae9d075 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4069,6 +4069,7 @@ void Driver::BuildJobs(Compilation &C) const {
           return;
         }
         OS << Buffer;
+        OS.flush();
       }
     });
   }