Index: src/main/java/javax/activation/MailcapCommandMap.java
===================================================================
--- src/main/java/javax/activation/MailcapCommandMap.java	(revision 21721)
+++ src/main/java/javax/activation/MailcapCommandMap.java	(working copy)
@@ -605,6 +605,11 @@
 		// if anything goes wrong, do it the old way
 		cl = Class.forName(name);
 	    }
+            if (!DataContentHandler.class.isAssignableFrom(cl)) {
+                if (LogSupport.isLoggable())
+                    LogSupport.log("DCH " + name + " is of invalid type");
+                return null;
+            }
 	    if (cl != null)		// XXX - always true?
 		return (DataContentHandler)cl.newInstance();
 	} catch (IllegalAccessException e) {