diff --git a/firmware/include/stdlib.h b/firmware/include/stdlib.h
index bf50c7e49e..40b5207223 100644
--- a/firmware/include/stdlib.h
+++ b/firmware/include/stdlib.h
@@ -30,7 +30,7 @@ void *calloc (size_t nmemb, size_t size);
 void free(void *);
 void *realloc(void *, size_t);
 
-#define abs(x) ((x)>0?x:-x)
+#define abs(x) ((x)>0?(x):-(x))
 
 #ifdef __cplusplus
 }