diff --git a/test/de/inetsoftware/jwebassembly/SpiderMonkeyTest.js b/test/de/inetsoftware/jwebassembly/SpiderMonkeyTest.js
index a1c1d89..2e30baa 100644
--- a/test/de/inetsoftware/jwebassembly/SpiderMonkeyTest.js
+++ b/test/de/inetsoftware/jwebassembly/SpiderMonkeyTest.js
@@ -6,7 +6,7 @@ function callExport(instance) {
     var result = {};
     for (var method in testData) {
         try{
-            result[method] = instance.exports[method]( ...testData[method] ).toString();
+            result[method] = String(instance.exports[method]( ...testData[method] ));
         }catch(err){
             result[method] = err.toString();
         }
diff --git a/test/de/inetsoftware/jwebassembly/SpiderMonkeyWatTest.js b/test/de/inetsoftware/jwebassembly/SpiderMonkeyWatTest.js
index f3e4781..077afb1 100644
--- a/test/de/inetsoftware/jwebassembly/SpiderMonkeyWatTest.js
+++ b/test/de/inetsoftware/jwebassembly/SpiderMonkeyWatTest.js
@@ -6,7 +6,7 @@ function callExport(instance) {
     var result = {};
     for (var method in testData) {
         try{
-            result[method] = instance.exports[method]( ...testData[method] ).toString();
+            result[method] = String(instance.exports[method]( ...testData[method] ));
         }catch(err){
             result[method] = err.toString();
         }
diff --git a/test/de/inetsoftware/jwebassembly/WatTest.js b/test/de/inetsoftware/jwebassembly/WatTest.js
index 02dccd4..90939ab 100644
--- a/test/de/inetsoftware/jwebassembly/WatTest.js
+++ b/test/de/inetsoftware/jwebassembly/WatTest.js
@@ -16,7 +16,7 @@ function callExport(instance) {
     var result = {};
     for (var method in testData) {
         try{
-            result[method] = instance.exports[method]( ...testData[method] ).toString();
+            result[method] = String(instance.exports[method]( ...testData[method] ));
         }catch(err){
             result[method] = err.toString();
         }
diff --git a/test/de/inetsoftware/jwebassembly/nodetest.js b/test/de/inetsoftware/jwebassembly/nodetest.js
index b93c0e4..0ab1f63 100644
--- a/test/de/inetsoftware/jwebassembly/nodetest.js
+++ b/test/de/inetsoftware/jwebassembly/nodetest.js
@@ -11,7 +11,7 @@ function callExport(instance) {
     var result = {};
     for (var method in testData) {
         try{
-            result[method] = instance.exports[method]( ...testData[method] ).toString();
+            result[method] = String(instance.exports[method]( ...testData[method] ));
         }catch(err){
             result[method] = err.toString();
         }