diff --git a/test/built-ins/String/prototype/trimEnd/this-value-object-toprimitive-returns-object-err.js b/test/built-ins/String/prototype/trimEnd/this-value-object-toprimitive-returns-object-err.js
index a40d97ba896cf62bf4cd58e92ec9c0e3ada81886..a9c572b0249313d044b194c286aabd894962cac5 100644
--- a/test/built-ins/String/prototype/trimEnd/this-value-object-toprimitive-returns-object-err.js
+++ b/test/built-ins/String/prototype/trimEnd/this-value-object-toprimitive-returns-object-err.js
@@ -33,6 +33,7 @@ var thisVal = {
   },
 };
 
+assert.sameValue(typeof String.prototype.trimEnd, 'function');
 assert.throws(TypeError, function() {
   String.prototype.trimEnd.call(thisVal);
 });
diff --git a/test/built-ins/String/prototype/trimEnd/this-value-object-tostring-returns-object-err.js b/test/built-ins/String/prototype/trimEnd/this-value-object-tostring-returns-object-err.js
index 2b4ed6006d73aba34fe98098910366b5655d1181..beb2296fe67ab7950e25e526d22df7023d6cb522 100644
--- a/test/built-ins/String/prototype/trimEnd/this-value-object-tostring-returns-object-err.js
+++ b/test/built-ins/String/prototype/trimEnd/this-value-object-tostring-returns-object-err.js
@@ -51,6 +51,7 @@ var thisVal = {
   },
 };
 
+assert.sameValue(typeof String.prototype.trimEnd, 'function');
 assert.throws(TypeError, function() {
   String.prototype.trimEnd.call(thisVal);
 });
diff --git a/test/built-ins/String/prototype/trimEnd/this-value-object-valueof-returns-object-err.js b/test/built-ins/String/prototype/trimEnd/this-value-object-valueof-returns-object-err.js
index 20a82731504ff640c196326862b944e4776df04b..36b182eeb5b8d2f19c64d5b8a9482884762d2943 100644
--- a/test/built-ins/String/prototype/trimEnd/this-value-object-valueof-returns-object-err.js
+++ b/test/built-ins/String/prototype/trimEnd/this-value-object-valueof-returns-object-err.js
@@ -52,6 +52,7 @@ var thisVal = {
   },
 };
 
+assert.sameValue(typeof String.prototype.trimEnd, 'function');
 assert.throws(TypeError, function() {
   String.prototype.trimEnd.call(thisVal);
 });
diff --git a/test/built-ins/String/prototype/trimStart/this-value-object-toprimitive-returns-object-err.js b/test/built-ins/String/prototype/trimStart/this-value-object-toprimitive-returns-object-err.js
index a5e0bf976fa7698d1a2703f4be28c299217dc7e5..d24157432dd85e95a9da2ed433a7ed36be222ed2 100644
--- a/test/built-ins/String/prototype/trimStart/this-value-object-toprimitive-returns-object-err.js
+++ b/test/built-ins/String/prototype/trimStart/this-value-object-toprimitive-returns-object-err.js
@@ -33,6 +33,7 @@ var thisVal = {
   },
 };
 
+assert.sameValue(typeof String.prototype.trimStart, 'function');
 assert.throws(TypeError, function() {
   String.prototype.trimStart.call(thisVal);
 });
diff --git a/test/built-ins/String/prototype/trimStart/this-value-object-tostring-returns-object-err.js b/test/built-ins/String/prototype/trimStart/this-value-object-tostring-returns-object-err.js
index 30ee4c751122ad8236f365a682425d99af0402ba..9c4377a815bb9a84cbbce7fb3f0b5be34ee24297 100644
--- a/test/built-ins/String/prototype/trimStart/this-value-object-tostring-returns-object-err.js
+++ b/test/built-ins/String/prototype/trimStart/this-value-object-tostring-returns-object-err.js
@@ -51,6 +51,7 @@ var thisVal = {
   },
 };
 
+assert.sameValue(typeof String.prototype.trimStart, 'function');
 assert.throws(TypeError, function() {
   String.prototype.trimStart.call(thisVal);
 });
diff --git a/test/built-ins/String/prototype/trimStart/this-value-object-valueof-returns-object-err.js b/test/built-ins/String/prototype/trimStart/this-value-object-valueof-returns-object-err.js
index 85cced2dca8affa6047166d7bc392eed2ec27292..77c184aca5c290ff5a8923b569adfb7e9a5d233f 100644
--- a/test/built-ins/String/prototype/trimStart/this-value-object-valueof-returns-object-err.js
+++ b/test/built-ins/String/prototype/trimStart/this-value-object-valueof-returns-object-err.js
@@ -52,6 +52,7 @@ var thisVal = {
   },
 };
 
+assert.sameValue(typeof String.prototype.trimStart, 'function');
 assert.throws(TypeError, function() {
   String.prototype.trimStart.call(thisVal);
 });