Less secure coders require explicit reference (e.g. mvg:my-graph.mvg)
diff --git a/coders/mvg.c b/coders/mvg.c
index cd6b7ad..7b09d08 100644
--- a/coders/mvg.c
+++ b/coders/mvg.c
@@ -250,6 +250,7 @@
   entry->decoder=(DecodeImageHandler *) ReadMVGImage;
   entry->encoder=(EncodeImageHandler *) WriteMVGImage;
   entry->magick=(IsImageFormatHandler *) IsMVG;
+  entry->format_type=ImplicitFormatType;
   entry->flags^=CoderAdjoinFlag;
   entry->flags|=CoderSeekableStreamFlag;
   (void) RegisterMagickInfo(entry);