diff --git a/src/screen.c b/src/screen.c
index b3220de..b4f55fe 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -17,7 +17,7 @@
  * ScreenLines[off]  Contains a copy of the whole screen, as it is currently
  *		     displayed (excluding text written by external commands).
  * ScreenAttrs[off]  Contains the associated attributes.
- * ScreenCols[off]   Contains the byte offset in the line. -1 means not
+ * ScreenCols[off]   Contains the virtual columns in the line. -1 means not
  *		     available (below last line), MAXCOL means after the end
  *		     of the line.
  *
@@ -743,7 +743,7 @@
 
 	ScreenCols[off_to] = ScreenCols[off_from];
 	if (char_cells == 2)
-	    ScreenCols[off_to + 1] = ScreenCols[off_from];
+	    ScreenCols[off_to + 1] = ScreenCols[off_from + 1];
 
 	off_to += char_cells;
 	off_from += char_cells;