diff --git a/Source/NSScroller.m b/Source/NSScroller.m
index 223e29f0a..2d893c6e6 100644
--- a/Source/NSScroller.m
+++ b/Source/NSScroller.m
@@ -382,6 +382,9 @@ static NSColor *scrollBarColor = nil;
       _knobProportion = ratio;
     }
 
+  /* Make sure we mark ourselves as needing redisplay.  */
+  _floatValue = -1;
+  
   [self setFloatValue: aFloat];
 }