Make sure that width or height don't animate to a negative value. Fixes #3881.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/fx.js b/src/fx.js
index d3a7ad404..15fce5c3a 100644
--- a/src/fx.js
+++ b/src/fx.js
@@ -432,7 +432,7 @@ jQuery.extend( jQuery.fx, {
 
 		_default: function(fx){
 			if ( fx.elem.style && fx.elem.style[ fx.prop ] != null ) {
-				fx.elem.style[ fx.prop ] = fx.now + fx.unit;
+				fx.elem.style[ fx.prop ] = (fx.prop === "width" || fx.prop === "height" ? Math.max(0, fx.now) : fx.now) + fx.unit;
 			} else {
 				fx.elem[ fx.prop ] = fx.now;
 			}