diff --git a/src/test/cpp/regression/makefile b/src/test/cpp/regression/makefile
index 76d43dc..59af8af 100644
--- a/src/test/cpp/regression/makefile
+++ b/src/test/cpp/regression/makefile
@@ -52,7 +52,7 @@ else
 endif
 
 ifeq ($(CONCURRENT_OS_EXECUTIONS),yes)
-	ADDCFLAGS += -CCONCURRENT_OS_EXECUTIONS
+	ADDCFLAGS += -CFLAGS -DCONCURRENT_OS_EXECUTIONS
 endif
 
 ifeq ($(LITEX),yes)