diff --git a/spec/stringProcessing/parseSynonymsSpec.js b/spec/stringProcessing/parseSynonymsSpec.js
index 2eccf5100..2d394a3b8 100644
--- a/spec/stringProcessing/parseSynonymsSpec.js
+++ b/spec/stringProcessing/parseSynonymsSpec.js
@@ -9,5 +9,6 @@ describe( "A test for parsing a comma-separated list of synonyms into an array o
 		expect( parseSynonyms( "!, ,?" ) ).toEqual( [] );
 		expect( parseSynonyms( "To be, or not to be, that is the question:" ) ).toEqual( [ "To be", "or not to be", "that is the question" ] );
 		expect( parseSynonyms( "To be,or not to be,that is the question:" ) ).toEqual( [ "To be", "or not to be", "that is the question" ] );
+		expect( parseSynonyms( null ) ).toEqual( [] );
 	} );
 } );
diff --git a/src/stringProcessing/parseSynonyms.js b/src/stringProcessing/parseSynonyms.js
index ad6c06901..ff69cd88e 100644
--- a/src/stringProcessing/parseSynonyms.js
+++ b/src/stringProcessing/parseSynonyms.js
@@ -11,6 +11,10 @@ const removePunctuation = require( "../stringProcessing/removePunctuation.js" );
  * @returns {Array} An array with all synonyms.
  */
 module.exports = function( synonyms ) {
+	if ( typeof synonyms !== "string" ) {
+		synonyms = "";
+	}
+
 	let synonymsSplit = synonyms.split( "," );
 
 	synonymsSplit = synonymsSplit.map( function( synonym ) {