diff --git a/src/xterm.c b/src/xterm.c
index 215a3ed3bbe..fd3e58f85f6 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -14699,7 +14699,7 @@ x_construct_mouse_click (struct input_event *result,
           result->kind = (event->type != ButtonRelease ? NO_EVENT
 		          : wheel & 2 ? HORIZ_WHEEL_EVENT : WHEEL_EVENT);
           result->code = 0;         /* Not used.  */
-          result->modifiers &= ~(up_modifier || down_modifier);
+          result->modifiers &= ~(up_modifier | down_modifier);
           result->modifiers |= wheel & 1 ? up_modifier : down_modifier;
         }
     }