diff --git a/src/buffer.c b/src/buffer.c
index 37182e1..0d14706 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4409,6 +4409,8 @@
     long	above; /* number of lines above window */
     long	below; /* number of lines below window */
 
+    if (buflen < 3) /* need at least 3 chars for writing */
+	return;
     above = wp->w_topline - 1;
 #ifdef FEAT_DIFF
     above += diff_check_fill(wp, wp->w_topline) - wp->w_topfill;