diff --git a/src/libauth/attr.c b/src/libauth/attr.c
index 5f35750..d8ad9ab 100644
--- a/src/libauth/attr.c
+++ b/src/libauth/attr.c
@@ -131,6 +131,9 @@
 	int i, ntok, type;
 	Attr *a;
 
+	if(s == nil)
+		return nil;
+
 	s = strdup(s);
 	if(s == nil)
 		sysfatal("_parseattr strdup: %r");