Index: wp-admin/js/revisions.js
===================================================================
--- wp-admin/js/revisions.js	(revision 24578)
+++ wp-admin/js/revisions.js	(working copy)
@@ -545,9 +545,7 @@
 
 			// And update the slider in case the route has set it.
 			this.updateSliderSettings();
-
 			this.slide( '', this.settings.attributes );
-
 			this.$el.slider( this.settings.toJSON() );
 
 			// Listen for changes in Compare Two Mode setting
@@ -568,7 +566,7 @@
 				actualX = e.clientX - sliderLeft,
 				hoveringAt = Math.floor( actualX / tickWidth );
 
-			// Reverse direction in Rtl mode.
+			// Reverse direction in RTL mode.
 			if ( isRtl )
 				hoveringAt = this.model.revisions.length - hoveringAt - 1;
 
@@ -606,7 +604,7 @@
 						rightValue = leftValue + 1;
 					}
 				} else {
-					leftValue  = isRtl ?	this.model.revisions.length -  this.model.revisions.indexOf( this.model.get( 'to' ) ) - 1 :
+					leftValue = isRtl ?	this.model.revisions.length - this.model.revisions.indexOf( this.model.get( 'to' ) ) - 1 :
 											this.model.revisions.indexOf( this.model.get( 'from' ) ),
 					rightValue = isRtl ?	this.model.revisions.length - this.model.revisions.indexOf( this.model.get( 'from' ) ) - 1 :
 											this.model.revisions.indexOf( this.model.get( 'to' ) );
@@ -665,23 +663,52 @@
 		},
 
 		start: function( event, ui ) {
-			if ( this.model.get( 'compareTwoMode' ) )
-				return;
-
+			var self = this;
 			// Track the mouse position to enable smooth dragging,
-			// overrides default jQuery UI step behaviour.
+			// overrides default jQuery UI step behavior.
 			$( window ).on( 'mousemove', { slider: this }, function( e ) {
-				var slider = e.data.slider,
-					sliderLeft = slider.$el.offset().left,
-					sliderRight = sliderLeft + slider.$el.width();
+				var slider            = e.data.slider,
+					leftDragBoundary  = slider.$el.offset().left, // Initial left boundary
+					sliderOffset      = leftDragBoundary,
+					sliderRightEdge   = leftDragBoundary + slider.$el.width(),
+					rightDragBoundary = sliderRightEdge, // Initial right boundary
+					leftDragReset     = 0, // Initial left drag reset
+					rightDragReset    = sliderRightEdge - sliderOffset; // Initial right drag reset
 
+				// In two handle mode, ensure handles can't be dragged past each other.
+				// Adjust left/right boundaries and reset points.
+				if ( self.model.get( 'compareTwoMode' ) ) {
+					var rightHandle = $(ui.handle).parent().find( '.right-handle' ),
+						leftHandle  = $(ui.handle).parent().find( '.left-handle' );
+					if ( $( ui.handle ).hasClass( 'left-handle' ) ) {
+						// Dragging the left handle, boundary is right handle.
+						// RTL mode calculations reverse directions.
+						if ( isRtl ) {
+							leftDragBoundary = rightHandle.offset().left + rightHandle.width();
+							leftDragReset    = leftDragBoundary - sliderOffset;
+						} else {
+							rightDragBoundary = rightHandle.offset().left;
+							rightDragReset    = rightDragBoundary - sliderOffset;
+						}
+					} else {
+						// Dragging the right handle, boundary is the left handle.
+						// RTL mode calculations reverse directions.
+						if ( isRtl ) {
+							rightDragBoundary = leftHandle.offset().left;
+							rightDragReset    = rightDragBoundary - sliderOffset;
+						} else {
+							leftDragBoundary = leftHandle.offset().left + leftHandle.width() ;
+							leftDragReset    = leftDragBoundary - sliderOffset;
+						}
+					}
+				}
 				// Follow mouse movements, as long as handle remains inside slider.
-				if ( e.clientX < sliderLeft ) {
-					$( ui.handle ).css( 'left', 0 ); // Mouse to left of slider.
-				} else if ( e.clientX > sliderRight ) {
-					$( ui.handle ).css( 'left', sliderRight - sliderLeft); // Mouse to right of slider.
+				if ( e.clientX < leftDragBoundary ) {
+					$( ui.handle ).css( 'left', leftDragReset ); // Mouse to left of slider.
+				} else if ( e.clientX > rightDragBoundary ) {
+					$( ui.handle ).css( 'left', rightDragReset); // Mouse to right of slider.
 				} else {
-					$( ui.handle ).css( 'left', e.clientX - sliderLeft ); // Mouse in slider.
+					$( ui.handle ).css( 'left', e.clientX - sliderOffset ); // Mouse in slider.
 				}
 			} );
 		},
@@ -716,9 +743,6 @@
 		},
 
 		stop: function( event, ui ) {
-			if ( this.model.get( 'compareTwoMode' ) )
-				return;
-
 			$( window ).off( 'mousemove' );
 
 			// Reset settings props handle back to the step position.