diff --git a/src/css.js b/src/css.js
index 75e74228c..c434fd1b7 100644
--- a/src/css.js
+++ b/src/css.js
@@ -22,7 +22,7 @@ var
 	// BuildExclude
 	getStyles = curCSS.getStyles,
 	ralpha = /alpha\([^)]*\)/i,
-	ropacity = /opacity\s*=\s*([^)]*)/,
+	ropacity = /opacity\s*=\s*([^)]*)/i,
 
 	// swappable if display is none or starts with table except
 	// "table", "table-cell", or "table-caption"
diff --git a/test/data/testsuite.css b/test/data/testsuite.css
index 545d8ce5d..d9909ddcc 100644
--- a/test/data/testsuite.css
+++ b/test/data/testsuite.css
@@ -156,3 +156,10 @@ section { background:#f0f; display:block; }
 #span-14824 { display: block; }
 
 #display { display: list-item !important; }
+
+/* fix get alpha opacity in IE8 */
+.fix-get-alpha-opacity-in-ie8 {
+	opacity: 0.5;
+	-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";
+}
+
diff --git a/test/unit/css.js b/test/unit/css.js
index 5121074fc..364249a31 100644
--- a/test/unit/css.js
+++ b/test/unit/css.js
@@ -1151,4 +1151,17 @@ test( "Do not throw on frame elements from css method (#15098)", 1, function() {
 		ok( false, "It did throw" );
 	}
 });
+
+test( "get upper case alpha opacity in IE8", 1, function() {
+	var div = document.createElement( "div" ),
+		fixture = document.getElementById( "qunit-fixture" );
+
+	div.className = "fix-get-alpha-opacity-in-ie8";
+	fixture.appendChild( div );
+
+	equal( jQuery( div ).css( "opacity" ), "0.5", "get upper case alpha opacity in IE8 ok" );
+
+	fixture.removeChild( div );
+});
+
 }