diff --git a/scheme/input-buffer.scm b/scheme/input-buffer.scm
index fcf6bd1..993a8cc 100644
--- a/scheme/input-buffer.scm
+++ b/scheme/input-buffer.scm
@@ -356,11 +356,13 @@
   (lambda (num-cols pos-col line)
     (let* ((lines (ceiling (/ (string-length line) num-cols)))
 	   (end-pos (* lines num-cols)))
-      (let loop ((offset 0)
-		 (end end-pos))
-	(if (< (+ end 2) pos-col)
-	    (- offset 1)
-	    (loop (+ offset 1) (- end num-cols)))))))
+      (if (= (string-length line) 0)
+	  0
+	  (let loop ((offset 0)
+		     (end end-pos))
+	    (if (<= (+ end 2) pos-col)
+		(- offset 1)
+		(loop (+ offset 1) (- end num-cols))))))))