diff --git a/src/ca/cadef.h b/src/ca/cadef.h
index 342f75d8c..924a13e32 100644
--- a/src/ca/cadef.h
+++ b/src/ca/cadef.h
@@ -738,7 +738,7 @@ typedef void CAFDHANDLER (void *parg, int fd, int opened);
 epicsShareFunc int epicsShareAPI ca_add_fd_registration
 (
      CAFDHANDLER    *pHandler,
-     const void     *pArg
+     void           *pArg
 );