diff --git a/karma.conf.js b/karma.conf.js
index 6d3047bb3b7..3495a981be9 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -135,17 +135,24 @@ module.exports = function (config) {
                     },
                 ],
                 noParse: [
+                    // for cross platform compatibility use [\\\/] as the path separator
+                    // this ensures that the regex trips on both Windows and *nix
+
                     // don't parse the languages within highlight.js. They
                     // cause stack overflows
                     // (https://github.com/webpack/webpack/issues/1721), and
                     // there is no need for webpack to parse them - they can
                     // just be included as-is.
-                    /highlight\.js\/lib\/languages/,
+                    /highlight\.js[\\\/]lib[\\\/]languages/,
+
+                    // olm takes ages for webpack to process, and it's already heavily
+                    // optimised, so there is little to gain by us uglifying it.
+                    /olm[\\\/](javascript[\\\/])?olm\.js$/,
 
                     // also disable parsing for sinon, because it
                     // tries to do voodoo with 'require' which upsets
                     // webpack (https://github.com/webpack/webpack/issues/304)
-                    /sinon\/pkg\/sinon\.js$/,
+                    /sinon[\\\/]pkg[\\\/]sinon\.js$/,
                 ],
             },
             resolve: {