diff --git a/stm/Makefile b/stm/Makefile
index 32f43213c3..7229f86e1e 100644
--- a/stm/Makefile
+++ b/stm/Makefile
@@ -18,7 +18,7 @@ DFU=../tools/dfu.py
 CROSS_COMPILE = arm-none-eabi-
 
 CFLAGS_CORTEX_M4 = -mthumb -mtune=cortex-m4 -mabi=aapcs-linux -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard -fsingle-precision-constant -Wdouble-promotion
-CFLAGS = -I. -I$(PY_SRC) -I$(CMSIS_DIR) -I$(STMPERIPH_DIR) -I$(STMUSB_DIR) -Wall -ansi -std=gnu99 $(CFLAGS_CORTEX_M4)
+CFLAGS = -I. -I$(PY_SRC) -I$(CMSIS_DIR) -I$(STMPERIPH_DIR) -I$(STMUSB_DIR) -Wall -ansi -std=gnu99 $(CFLAGS_CORTEX_M4) $(COPT)
 CFLAGS += -I$(STMUSBD_DIR)
 CFLAGS += -I$(STMUSBH_DIR)
 CFLAGS += -I$(FATFS_DIR)
@@ -26,9 +26,10 @@ CFLAGS += -I$(FATFS_DIR)
 
 #Debugging/Optimization
 ifeq ($(DEBUG), 1)
-CFLAGS += -O0 -ggdb
+CFLAGS += -g
+COPT = -O0
 else
-CFLAGS += -Os -DNDEBUG
+COPT += -Os -DNDEBUG
 endif
 
 LDFLAGS = --nostdlib -T stm32f405.ld -Map=$(@:.elf=.map) --cref