diff --git a/Mac/Python/macguesstabsize.c b/Mac/Python/macguesstabsize.c
index 43af8845fdd..64a6ad7c6e7 100644
--- a/Mac/Python/macguesstabsize.c
+++ b/Mac/Python/macguesstabsize.c
@@ -45,6 +45,9 @@ guesstabsize(path)
 	int refnum;
 	Handle h;
 	int tabsize = 0;
+	
+	/* Very simple case: stdin (pathname empty) */
+	if ( path[0] == '\0' || strcmp(path, "<stdin>") == 0 ) return 0;
 	s[0] = strlen(path);
 	memcpy(s+1, path, s[0]);
 	refnum = OpenResFile(s);