Index: generic/tclIO.c
==================================================================
--- generic/tclIO.c
+++ generic/tclIO.c
@@ -7714,11 +7714,11 @@
 	 * have occurred on the channel, invoke its procedure.
 	 */
 
 	if ((chPtr->mask & mask) != 0) {
 	    nh.nextHandlerPtr = chPtr->nextPtr;
-	    (*(chPtr->proc))(chPtr->clientData, mask);
+	    (*(chPtr->proc))(chPtr->clientData, chPtr->mask & mask);
 	    chPtr = nh.nextHandlerPtr;
 	} else {
 	    chPtr = chPtr->nextPtr;
 	}
     }