diff --git a/src/frame.c b/src/frame.c
index c42e2ab..5d18218 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -190,7 +190,7 @@ frame_dump (rp_frame *frame, rp_screen *screen)
 }
 
 /* Used only by frame_read */
-#define read_slot(x) do { tmp = strtok_ws (NULL); x = strtol(tmp,NULL,10); } while(0)
+#define read_slot(x) do { tmp = strtok_ws (NULL); x = tmp?strtol(tmp,NULL,10):0; } while(0)
 
 rp_frame *
 frame_read (char *str, rp_screen *screen)