diff --git a/src/output.jl b/src/output.jl
index b8e95bb7..003deec4 100644
--- a/src/output.jl
+++ b/src/output.jl
@@ -103,7 +103,7 @@ end
 function addExtension(fn::AbstractString, ext::AbstractString)
   try
     oldext = getExtension(fn)
-    if _savemap[oldext] == ext
+    if string(_savemap[oldext]) == ext
       return fn
     else
       return "$fn.$ext"