diff --git a/crypto/engine/eng_dyn.c b/crypto/engine/eng_dyn.c
index 61ae23057..3a1c200ce 100644
--- a/crypto/engine/eng_dyn.c
+++ b/crypto/engine/eng_dyn.c
@@ -70,7 +70,7 @@
 /* Our ENGINE handlers */
 static int dynamic_init(ENGINE *e);
 static int dynamic_finish(ENGINE *e);
-static int dynamic_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)());
+static int dynamic_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void));
 /* Predeclare our context type */
 typedef struct st_dynamic_data_ctx dynamic_data_ctx;
 /* The implementation for the important control command */