diff --git a/tools/llvm-config/Makefile b/tools/llvm-config/Makefile
index 55e3b568a4b..d885c163929 100644
--- a/tools/llvm-config/Makefile
+++ b/tools/llvm-config/Makefile
@@ -57,7 +57,7 @@ llvm-config.in: $(ConfigInIn) $(ConfigStatusScript)
 $(ToolDir)/llvm-config: llvm-config.in $(FinalLibDeps)
 	$(Echo) "Building llvm-config script."
 	$(Verb) $(ECHO) 's,@LLVM_CFLAGS@,$(SUB_CFLAGS),' > temp.sed
-	$(Verb) $(ECHO) 's,@LLVM_CXXFLAGS@,$(SUB_CXXFLAGS),' > temp.sed
+	$(Verb) $(ECHO) 's,@LLVM_CXXFLAGS@,$(SUB_CXXFLAGS),' >> temp.sed
 	$(Verb) $(ECHO) 's,@LLVM_LDFLAGS@,$(SUB_LDFLAGS),' >> temp.sed
 	$(Verb) $(ECHO) 's,@LLVM_BUILDMODE@,$(BuildMode),' >> temp.sed
 	$(Verb) $(SED) -f temp.sed < $< > $@