diff -r 942deef87200 -r 146ae7b52b64 dew/src/main/java/org/apidesign/bck2brwsr/dew/Compile.java
--- a/dew/src/main/java/org/apidesign/bck2brwsr/dew/Compile.java	Fri Jan 25 10:25:30 2013 +0100
+++ b/dew/src/main/java/org/apidesign/bck2brwsr/dew/Compile.java	Tue Apr 02 15:40:51 2013 +0200
@@ -158,7 +158,20 @@
                 
                 return null;
             }
-            
+
+            @Override
+            public boolean isSameFile(FileObject a, FileObject b) {
+                if (a == null || b == null) {
+                    throw new NullPointerException();
+                }
+                if (!(a instanceof SimpleJavaFileObject)) {
+                    throw new IllegalArgumentException("Not supported: " + a);
+                }
+                if (!(b instanceof SimpleJavaFileObject)) {
+                    throw new IllegalArgumentException("Not supported: " + b);
+                }
+                return a.equals(b);
+            }
         };
 
         ToolProvider.getSystemJavaCompiler().getTask(null, jfm, this, /*XXX:*/Arrays.asList("-source", "1.7", "-target", "1.7"), null, Arrays.asList(file)).call();