diff --git a/src/input/input_ebml.h b/src/input/input_ebml.h
index 10f3a700..4b433f0c 100644
--- a/src/input/input_ebml.h
+++ b/src/input/input_ebml.h
@@ -128,7 +128,7 @@ namespace Mist{
       readHeader();
     }
     bool openStreamSource(){return true;}
-    bool needHeader(){return needsLock();}
+    bool needHeader(){return needsLock() && !readExistingHeader();}
     double timeScale;
   };
 }