diff --git a/firmware/common/sprintf.h b/firmware/common/sprintf.h
index 548127a4df..be79683368 100644
--- a/firmware/common/sprintf.h
+++ b/firmware/common/sprintf.h
@@ -20,6 +20,6 @@
 #ifndef __SPRINTF_H__
 #define __SPRINTF_H__
 
-int snprintf (char *buf, int size, const char *fmt, ...);
+int snprintf (char *buf, size_t size, const char *fmt, ...);
 
-#endif /* __SPRINTF_H__ */
\ No newline at end of file
+#endif /* __SPRINTF_H__ */