diff --git a/src/main/org/apache/tools/ant/taskdefs/optional/extension/ExtensionUtil.java b/src/main/org/apache/tools/ant/taskdefs/optional/extension/ExtensionUtil.java
index d6cb01c5a..4ed4cdd58 100644
--- a/src/main/org/apache/tools/ant/taskdefs/optional/extension/ExtensionUtil.java
+++ b/src/main/org/apache/tools/ant/taskdefs/optional/extension/ExtensionUtil.java
@@ -238,7 +238,11 @@ public class ExtensionUtil {
         throws BuildException {
         try {
             final JarFile jarFile = new JarFile(file);
-            return jarFile.getManifest();
+            Manifest m = jarFile.getManifest();
+            if (m == null) {
+                throw new BuildException(file + " doesn't have a MANIFEST");
+            }
+            return m;
         } catch (final IOException ioe) {
             throw new BuildException(ioe.getMessage(), ioe);
         }