Index: src/hg/lib/hgMaf.c
===================================================================
RCS file: /projects/compbio/cvsroot/kent/src/hg/lib/hgMaf.c,v
retrieving revision 1.13
retrieving revision 1.14
diff -b -B -U 4 -r1.13 -r1.14
--- src/hg/lib/hgMaf.c	10 Apr 2009 19:52:43 -0000	1.13
+++ src/hg/lib/hgMaf.c	9 Apr 2010 00:12:00 -0000	1.14
@@ -46,8 +46,10 @@
     struct scoredRef ref;
     scoredRefStaticLoad(row + rowOffset, &ref);
     if ((file != NULL) && (ref.extFile != 0))
 	errAbort("expect extFile to be zero if file specified\n");
+    if ((file == NULL) && (ref.extFile == 0))
+	errAbort("expect extFile to be not zero or file specified\n");
 
     if (ref.extFile != extFileId)
 	{
 	char *path = hExtFileNameC(conn2, "extFile", ref.extFile);

