diff --git a/src/css/support.js b/src/css/support.js
index 1078c0905..4a8fc87ac 100644
--- a/src/css/support.js
+++ b/src/css/support.js
@@ -94,11 +94,10 @@ define([
 
 		// Support: IE<9
 		// Assume reasonable values in the absence of getComputedStyle
-		pixelPositionVal = false;
-		reliableMarginRightVal = boxSizingReliableVal = true;
+		pixelPositionVal = boxSizingReliableVal = false;
+		reliableMarginRightVal = true;
 
-		// Support: node.js jsdom
-		// Don't assume that getComputedStyle is a property of the global object
+		// Check for getComputedStyle so that this code is not run in IE<9.
 		if ( window.getComputedStyle ) {
 			pixelPositionVal = ( window.getComputedStyle( div, null ) || {} ).top !== "1%";
 			boxSizingReliableVal =
diff --git a/test/unit/support.js b/test/unit/support.js
index eae4c2025..c1f9d9bb9 100644
--- a/test/unit/support.js
+++ b/test/unit/support.js
@@ -267,7 +267,7 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 			"ajax": true,
 			"appendChecked": true,
 			"boxSizing": true,
-			"boxSizingReliable": true,
+			"boxSizingReliable": false,
 			"changeBubbles": false,
 			"checkClone": true,
 			"checkOn": true,
@@ -304,7 +304,7 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 			"ajax": true,
 			"appendChecked": false,
 			"boxSizing": false,
-			"boxSizingReliable": true,
+			"boxSizingReliable": false,
 			"changeBubbles": false,
 			"checkClone": true,
 			"checkOn": true,
@@ -341,7 +341,7 @@ testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Sec
 			"ajax": true,
 			"appendChecked": false,
 			"boxSizing": false,
-			"boxSizingReliable": true,
+			"boxSizingReliable": false,
 			"changeBubbles": false,
 			"checkClone": true,
 			"checkOn": true,