diff --git a/src/shared/compatibility.js b/src/shared/compatibility.js
index 10a2065c0..0af66a21e 100644
--- a/src/shared/compatibility.js
+++ b/src/shared/compatibility.js
@@ -21,9 +21,10 @@ if ((typeof PDFJSDev === 'undefined' ||
      !PDFJSDev.test('FIREFOX || MOZCENTRAL || CHROME')) &&
     (typeof PDFJS === 'undefined' || !PDFJS.compatibilityChecked)) {
 
-var globalScope = (typeof window !== 'undefined') ? window :
-                  (typeof global !== 'undefined') ? global :
-                  (typeof self !== 'undefined') ? self : this;
+var globalScope =
+  (typeof window !== 'undefined' && window.Math === Math) ? window :
+  (typeof global !== 'undefined' && global.Math === Math) ? global :
+  (typeof self !== 'undefined' && self.Math === Math) ? self : this;
 
 var userAgent = (typeof navigator !== 'undefined' && navigator.userAgent) || '';
 var isAndroid = /Android/.test(userAgent);
diff --git a/src/shared/util.js b/src/shared/util.js
index bde41df2f..e338adbe6 100644
--- a/src/shared/util.js
+++ b/src/shared/util.js
@@ -17,9 +17,10 @@
 import './compatibility';
 import { ReadableStream } from '../../external/streams/streams-lib';
 
-var globalScope = (typeof window !== 'undefined') ? window :
-                  (typeof global !== 'undefined') ? global :
-                  (typeof self !== 'undefined') ? self : this;
+var globalScope =
+  (typeof window !== 'undefined' && window.Math === Math) ? window :
+  (typeof global !== 'undefined' && global.Math === Math) ? global :
+  (typeof self !== 'undefined' && self.Math === Math) ? self : this;
 
 var FONT_IDENTITY_MATRIX = [0.001, 0, 0, 0.001, 0, 0];