diff --git a/sw/ext/Makefile b/sw/ext/Makefile
index c3783d5f070..bd5ccd0000d 100644
--- a/sw/ext/Makefile
+++ b/sw/ext/Makefile
@@ -48,7 +48,7 @@ endif
 all: libopencm3.module stm32loader.module
 
 libopencm3.module:
-	$(Q)if [ ! -f $(PAPARAZZI_SRC)/libopencm3/Makefile ]; then \
+	$(Q)if [ ! -f $(EXT_DIR)/libopencm3/Makefile ]; then \
 		cd $(PAPARAZZI_SRC); \
 		git submodule init; \
 		git submodule update; \
@@ -57,12 +57,12 @@ libopencm3.module:
 	make -C libopencm3 lib PREFIX=$(PREFIX)
 
 stm32loader.module:
-	$(Q)if [ ! -f $(PAPARAZZI_SRC)/stm32loader/stm32loader/py ]; then \
-                cd $(PAPARAZZI_SRC); \
-                git submodule init; \
-                git submodule update; \
-                cd -; \
-        fi
+	$(Q)if [ ! -f $(EXT_DIR)/stm32loader/stm32loader.py ]; then \
+		cd $(PAPARAZZI_SRC); \
+		git submodule init; \
+		git submodule update; \
+		cd -; \
+	fi
 
 clean:
 	if [ -f libopencm3/Makefile ]; then \