diff --git a/libfprint/drivers/vfs301_proto.c b/libfprint/drivers/vfs301_proto.c
index 2bf8bbd2..c272659f 100644
--- a/libfprint/drivers/vfs301_proto.c
+++ b/libfprint/drivers/vfs301_proto.c
@@ -177,6 +177,7 @@ translate_str (const char **srcL, gssize *len)
       src_len += tmp;
     }
 
+  g_assert (src_len >= 2);
   *len = src_len / 2;
   res = g_malloc0 (*len);
   dst = res;