diff --git a/src/if_tcl.c b/src/if_tcl.c
index 9e7cd4c..1882b41 100644
--- a/src/if_tcl.c
+++ b/src/if_tcl.c
@@ -180,7 +180,7 @@
  * Declare HANDLE for tcl.dll and function pointers.
  */
 static HANDLE hTclLib = NULL;
-Tcl_Interp* (*dll_Tcl_CreateInterp)();
+Tcl_Interp* (*dll_Tcl_CreateInterp)(void);
 void (*dll_Tcl_FindExecutable)(const void *);
 
 /*