diff --git a/firmware/include/stdio.h b/firmware/include/stdio.h
index 968bd59aab..dd22f7d5b1 100644
--- a/firmware/include/stdio.h
+++ b/firmware/include/stdio.h
@@ -39,6 +39,7 @@ int vsnprintf (char *buf, int size, const char *fmt, __VALIST ap);
 #ifdef SIMULATOR
 typedef void FILE;
 int vfprintf(FILE *stream, const char *format, __VALIST ap);
+int fprintf(FILE *stream, const char *format, ...);
 #ifdef WIN32
 #define FILENAME_MAX 260 /* ugly hard-coded value of a limit that is set
                             in file.h */