diff --git a/testcases/test-builtin-string-proto-trim.js b/testcases/test-builtin-string-proto-trim.js
index 4e6902cb..e37cedd8 100644
--- a/testcases/test-builtin-string-proto-trim.js
+++ b/testcases/test-builtin-string-proto-trim.js
@@ -42,12 +42,15 @@ var WHITESPACE_CODEPOINTS = [
 ];
 
 /*===
+basic
 string 3 foo
 string 3 foo
 string 3 foo
 string 3 foo
 ===*/
 
+print('basic');
+
 function basicTest() {
     var all_ws;
     var i;
@@ -61,7 +64,7 @@ function basicTest() {
 
     all_ws = [];
     for (i = 0; i < WHITESPACE_CODEPOINTS; i++) {
-        all_ws.push(String.fromCharCode(i));
+        all_ws.push(String.fromCharCode(WHITESPACE_CODEPOINTS[i]));
     }
     all_ws = all_ws.join('');
 
@@ -77,3 +80,51 @@ try {
     print(e);
 }
 
+/*===
+coercion
+TypeError
+TypeError
+TypeError
+string 4 true
+string 5 false
+string 3 123
+string 3 foo
+string 3 1,2
+string 15 [object Object]
+===*/
+
+print('coercion');
+
+function coercionTest() {
+    function test(this_val, arg_count) {
+        var t;
+
+        try {
+            if (arg_count == 0) {
+                t = String.prototype.trim.call();
+            } else {
+                t = String.prototype.trim.call(this_val);
+            }
+            print(typeof t, t.length, t);
+        } catch (e) {
+            print(e.name);
+        }
+    }
+
+    test(undefined, 0);
+    test(undefined);
+    test(null);
+    test(true);
+    test(false);
+    test(123);
+    test('foo');
+    test([1,2]);
+    test({ foo: 1, bar: 2 });
+}
+
+try {
+    coercionTest();
+} catch (e) {
+    print(e);
+}
+