diff --git a/lib/themeroller.js b/lib/themeroller.js
index 98544c7..21e3b50 100644
--- a/lib/themeroller.js
+++ b/lib/themeroller.js
@@ -98,16 +98,18 @@ function ThemeRoller( baseThemeCss, vars, options ) {
 	vars.opacityShadowPerc = vars.opacityShadow;
 	if ( options.version && semver.lt( options.version, "1.10.0" ) ) {
 
-		// For version < 1.10.0, opacity (w3c) and filter (IE) are combined into the same line.
+		// For version <1.10.0, opacity (w3c) and filter (IE) are combined
+		// into the same line.
 		opacityFix = function( opacity ) {
 			return /* w3c */ ( opacity / 100 ).toString().replace( /^0\./, "." ) + /* IE */ ";filter:Alpha(Opacity=" + opacity + ")";
 		};
 		vars.opacityOverlay = opacityFix( vars.opacityOverlay );
 		vars.opacityShadow = opacityFix( vars.opacityShadow );
 
-	} else {
+	} else if ( options.version && semver.lt( options.version, "1.13.0" ) ) {
 
-		// For version >= 1.10.0, filter has its own separate line and variable name.
+		// For version >=1.10.0, `filter` has its own separate line
+		// and variable name.
 		opacityFix = function( opacity ) {
 			return ( opacity / 100 ).toString().replace( /^0\./, "." );
 		};
@@ -118,6 +120,21 @@ function ThemeRoller( baseThemeCss, vars, options ) {
 		vars.opacityFilterShadow = opacityFilter( vars.opacityShadow );
 		vars.opacityOverlay = opacityFix( vars.opacityOverlay );
 		vars.opacityShadow = opacityFix( vars.opacityShadow );
+
+	} else {
+
+		// For version >=1.13.0, `-ms-filter` has its own separate line
+		// and variable name.
+		opacityFix = function( opacity ) {
+			return ( opacity / 100 ).toString().replace( /^0\./, "." );
+		};
+		opacityFilter = function( opacity ) {
+			return "\"alpha(opacity=" + opacity + ")\"";
+		};
+		vars.opacityFilterOverlay = opacityFilter( vars.opacityOverlay );
+		vars.opacityFilterShadow = opacityFilter( vars.opacityShadow );
+		vars.opacityOverlay = opacityFix( vars.opacityOverlay );
+		vars.opacityShadow = opacityFix( vars.opacityShadow );
 	}
 
 	// Add '#' in the beginning of the colors if needed
diff --git a/test/fixtures/jquery-ui-1.13.2/themes/smoothness.css b/test/fixtures/jquery-ui-1.13.2/themes/smoothness.css
index e4fa82c..8388761 100644
--- a/test/fixtures/jquery-ui-1.13.2/themes/smoothness.css
+++ b/test/fixtures/jquery-ui-1.13.2/themes/smoothness.css
@@ -438,7 +438,7 @@ a.ui-button:active,
 .ui-widget-overlay {
 	background: #aaaaaa;
 	opacity: .3;
-	-ms-filter: Alpha(Opacity=30); /* support: IE8 */
+	-ms-filter: "alpha(opacity=30)"; /* support: IE8 */
 }
 .ui-widget-shadow {
 	-webkit-box-shadow: -8px -8px 8px #aaaaaa;