diff --git a/fml/src/main/java/cpw/mods/fml/relauncher/CoreModManager.java b/fml/src/main/java/cpw/mods/fml/relauncher/CoreModManager.java
index f3f05a3f7..8704b22c1 100644
--- a/fml/src/main/java/cpw/mods/fml/relauncher/CoreModManager.java
+++ b/fml/src/main/java/cpw/mods/fml/relauncher/CoreModManager.java
@@ -223,6 +223,22 @@ public class CoreModManager {
                 return name.endsWith(".jar");
             }
         };
+        FilenameFilter derpfilter = new FilenameFilter() {
+            @Override
+            public boolean accept(File dir, String name)
+            {
+                return name.endsWith(".jar.zip");
+            }
+        };
+        File[] derplist = coreMods.listFiles(derpfilter);
+        if (derplist != null && derplist.length > 0)
+        {
+        	FMLRelaunchLog.severe("FML has detected several badly downloaded jar files,  which have been named as zip files. You probably need to download them again, or they may not work properly");
+        	for (File f : derplist)
+        	{
+        		FMLRelaunchLog.severe("Problem file : %s", f.getName());
+        	}
+        }
         File[] coreModList = coreMods.listFiles(ff);
         File versionedModDir = new File(coreMods, FMLInjectionData.mccversion);
         if (versionedModDir.isDirectory())