diff --git a/src/util.h b/src/util.h
index 0921e34f16..9447f31b5b 100644
--- a/src/util.h
+++ b/src/util.h
@@ -13,9 +13,12 @@
 
 #include <stdlib.h>
 #include <stdint.h>
-#include <stdio.h>
 #include <limits.h>
 
+#ifndef USE_EXTERNAL_DEFAULT_CALLBACKS
+#include <stdio.h>              /* for fprintf */
+#endif
+
 #define STR_(x) #x
 #define STR(x) STR_(x)
 #define DEBUG_CONFIG_MSG(x) "DEBUG_CONFIG: " x