diff --git a/STM32/cores/arduino/itoa.h b/STM32/cores/arduino/itoa.h
index 59af109..58556b7 100644
--- a/STM32/cores/arduino/itoa.h
+++ b/STM32/cores/arduino/itoa.h
@@ -28,10 +28,15 @@ extern "C"{
 extern void itoa( int n, char s[] ) ;
 
 #else
+    
+#if __GNUC__ < 5
+
+extern char* utoa( unsigned long value, char *string, int radix ) ;
+
+#endif
 
 extern char* itoa( int value, char *string, int radix ) ;
 extern char* ltoa( long value, char *string, int radix ) ;
-extern char* utoa( unsigned long value, char *string, int radix ) ;
 extern char* ultoa( unsigned long value, char *string, int radix ) ;
 #endif /* 0 */