diff --git a/include/cbm.h b/include/cbm.h
index 5bb860e4f..cdbd7b886 100644
--- a/include/cbm.h
+++ b/include/cbm.h
@@ -161,6 +161,11 @@ unsigned char kbrepeat(unsigned char);
 unsigned char kbrepeatdelay(unsigned char);
 unsigned char kbrepeatrate(unsigned char);
 
+#if !defined(__CBM610__) && !defined(__PET__)
+void waitvsync (void);
+/* wait for the start of the next frame */
+#endif
+
 /*****************************************************************************/
 /*                           CBM kernal functions                            */
 /*****************************************************************************/