diff --git a/tools/lib/subcmd/Makefile b/tools/lib/subcmd/Makefile
index 5b2cd5e58df09d11c94a939173ab2fce7826bb22..5dbb0dde208c4bcef8316d3811515a70ddac533a 100644
--- a/tools/lib/subcmd/Makefile
+++ b/tools/lib/subcmd/Makefile
@@ -28,7 +28,9 @@ 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