diff --git a/targets/stm32l432/build/application.mk b/targets/stm32l432/build/application.mk
index c64e9cf..9fe649f 100644
--- a/targets/stm32l432/build/application.mk
+++ b/targets/stm32l432/build/application.mk
@@ -81,4 +81,4 @@ cbor:
 	cd ../../tinycbor/ && make clean
 	cd ../../tinycbor/ && make CC="$(CC)" AR=$(AR) \
 LDFLAGS="$(LDFLAGS_LIB)" \
-CFLAGS="$(CFLAGS)"
+CFLAGS="$(CFLAGS) -Os"