diff --git a/tools/lib/subcmd/Makefile b/tools/lib/subcmd/Makefile
index 352c6062deba..1c777a72bb39 100644
--- a/tools/lib/subcmd/Makefile
+++ b/tools/lib/subcmd/Makefile
@@ -27,7 +27,9 @@ ifeq ($(DEBUG),0)
   endif
 endif
 
-ifeq ($(CC_NO_CLANG), 0)
+ifeq ($(DEBUG),1)
+  CFLAGS += -O0
+else ifeq ($(CC_NO_CLANG), 0)
   CFLAGS += -O3
 else
   CFLAGS += -O6