diff --git a/jetty-util/src/test/java/org/eclipse/jetty/util/Utf8StringBuilderTest.java b/jetty-util/src/test/java/org/eclipse/jetty/util/Utf8StringBuilderTest.java
index 7ff2eb9fd6c..84166df5882 100644
--- a/jetty-util/src/test/java/org/eclipse/jetty/util/Utf8StringBuilderTest.java
+++ b/jetty-util/src/test/java/org/eclipse/jetty/util/Utf8StringBuilderTest.java
@@ -16,6 +16,7 @@ package org.eclipse.jetty.util;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
+import org.junit.Assert;
 import org.junit.Test;
 
 public class Utf8StringBuilderTest
@@ -35,14 +36,38 @@ public class Utf8StringBuilderTest
                 Utf8StringBuilder buffer = new Utf8StringBuilder();
                 buffer.append(bytes,0,bytes.length);
 
-                assertEquals(i,"not expected",buffer.toString());
+                Assert.fail("Should have thrown a NotUtf8Exception");
             }
             catch (Utf8Appendable.NotUtf8Exception e)
             {
-                assertTrue(i,true);
+                // expected path
             }
         }
     }
+    
+    @Test
+    public void testFastFail() throws Exception
+    {
+        byte[] part1 = TypeUtil.fromHexString("cebae1bdb9cf83cebcceb5");
+        byte[] part2 = TypeUtil.fromHexString("f4908080"); // INVALID
+        byte[] part3 = TypeUtil.fromHexString("656469746564");
+
+        Utf8StringBuilder buffer = new Utf8StringBuilder();
+        // Part 1 is valid
+        buffer.append(part1,0,part1.length);
+        try
+        {
+            // Part 2 is invalid
+            buffer.append(part2,0,part2.length);
+            Assert.fail("Should have thrown a NotUtf8Exception");
+        }
+        catch (Utf8Appendable.NotUtf8Exception e)
+        {
+            // expected path
+        }
+        // Part 3 is valid
+        buffer.append(part3,0,part3.length);
+    }
 
     @Test
     public void testUtfStringBuilder() throws Exception
@@ -78,13 +103,14 @@ public class Utf8StringBuilderTest
         Utf8StringBuilder buffer = new Utf8StringBuilder();
         try
         {
-            for (byte aByte : bytes)
+            for (byte aByte : bytes) {
                 buffer.append(aByte);
-            assertTrue(false);
+            }
+            Assert.fail("Should have resulted in an Utf8Appendable.NotUtf8Exception");
         }
-        catch (IllegalArgumentException e)
+        catch (Utf8Appendable.NotUtf8Exception e)
         {
-            assertTrue(true);
+            // expected path
         }
         assertEquals("abc\ufffd",buffer.toString());
     }