diff --git a/src/core/config/modules/CharEnc.js b/src/core/config/modules/CharEnc.js
index 2674f973..4c27ebed 100644
--- a/src/core/config/modules/CharEnc.js
+++ b/src/core/config/modules/CharEnc.js
@@ -12,7 +12,7 @@ import CharEnc from "../../operations/CharEnc.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.CharEnc = {
     "Encode text": CharEnc.runEncode,
diff --git a/src/core/config/modules/Ciphers.js b/src/core/config/modules/Ciphers.js
index f4c7c424..de7e1f20 100644
--- a/src/core/config/modules/Ciphers.js
+++ b/src/core/config/modules/Ciphers.js
@@ -12,7 +12,7 @@ import Cipher from "../../operations/Cipher.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Ciphers = {
     "AES Encrypt":          Cipher.runAesEnc,
diff --git a/src/core/config/modules/Code.js b/src/core/config/modules/Code.js
index eb7496d1..6398174b 100644
--- a/src/core/config/modules/Code.js
+++ b/src/core/config/modules/Code.js
@@ -16,7 +16,7 @@ import Code from "../../operations/Code.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Code = {
     "JavaScript Parser":     JS.runParse,
diff --git a/src/core/config/modules/Compression.js b/src/core/config/modules/Compression.js
index 98c09859..aa8d074f 100644
--- a/src/core/config/modules/Compression.js
+++ b/src/core/config/modules/Compression.js
@@ -12,7 +12,7 @@ import Compress from "../../operations/Compress.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Compression = {
     "Raw Deflate":      Compress.runRawDeflate,
diff --git a/src/core/config/modules/Default.js b/src/core/config/modules/Default.js
index 127ebf61..7513be4a 100644
--- a/src/core/config/modules/Default.js
+++ b/src/core/config/modules/Default.js
@@ -42,7 +42,7 @@ import UUID from "../../operations/UUID.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Default = {
     "To Hexdump":           Hexdump.runTo,
diff --git a/src/core/config/modules/Diff.js b/src/core/config/modules/Diff.js
index 5c165a47..e6888a3a 100644
--- a/src/core/config/modules/Diff.js
+++ b/src/core/config/modules/Diff.js
@@ -11,7 +11,7 @@ import Diff from "../../operations/Diff.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Diff = {
     "Diff": Diff.runDiff,
diff --git a/src/core/config/modules/Encodings.js b/src/core/config/modules/Encodings.js
index 0b309fae..c029117c 100644
--- a/src/core/config/modules/Encodings.js
+++ b/src/core/config/modules/Encodings.js
@@ -11,7 +11,7 @@ import Punycode from "../../operations/Punycode.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Encodings = {
     "To Punycode":   Punycode.runToAscii,
diff --git a/src/core/config/modules/HTTP.js b/src/core/config/modules/HTTP.js
index 3cf293ae..8972a3e6 100644
--- a/src/core/config/modules/HTTP.js
+++ b/src/core/config/modules/HTTP.js
@@ -11,7 +11,7 @@ import HTTP from "../../operations/HTTP.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.HTTP = {
     "HTTP request":       HTTP.runHTTPRequest,
diff --git a/src/core/config/modules/Hashing.js b/src/core/config/modules/Hashing.js
index aa7ac18c..f9debf45 100644
--- a/src/core/config/modules/Hashing.js
+++ b/src/core/config/modules/Hashing.js
@@ -14,7 +14,7 @@ import Hash from "../../operations/Hash.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Hashing = {
     "Analyse hash":         Hash.runAnalyse,
diff --git a/src/core/config/modules/Image.js b/src/core/config/modules/Image.js
index 0479b9a9..7ce03cba 100644
--- a/src/core/config/modules/Image.js
+++ b/src/core/config/modules/Image.js
@@ -13,7 +13,7 @@ import Image from "../../operations/Image.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.Image = {
     "Extract EXIF": Image.runExtractEXIF,
diff --git a/src/core/config/modules/JSBN.js b/src/core/config/modules/JSBN.js
index 5d756c9f..53718924 100644
--- a/src/core/config/modules/JSBN.js
+++ b/src/core/config/modules/JSBN.js
@@ -13,7 +13,7 @@ import Filetime from "../../operations/Filetime.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.JSBN = {
     "Parse IP range":     IP.runParseIpRange,
diff --git a/src/core/config/modules/PublicKey.js b/src/core/config/modules/PublicKey.js
index 6af357a8..cbf46ccc 100644
--- a/src/core/config/modules/PublicKey.js
+++ b/src/core/config/modules/PublicKey.js
@@ -11,7 +11,7 @@ import PublicKey from "../../operations/PublicKey.js";
  * @copyright Crown Copyright 2017
  * @license Apache-2.0
  */
-let OpModules = self.OpModules || {};
+let OpModules = typeof self === "undefined" ? {} : self.OpModules || {};
 
 OpModules.PublicKey = {
     "Parse X.509 certificate":  PublicKey.runParseX509,