diff --git a/src/mark.c b/src/mark.c
index dd714d8..c7395f3 100644
--- a/src/mark.c
+++ b/src/mark.c
@@ -686,10 +686,11 @@
 
     if (mp->lnum == 0 || mp->lnum > curbuf->b_ml.ml_line_count)
 	return vim_strsave((char_u *)"-invalid-");
-    s = vim_strnsave(skipwhite(ml_get(mp->lnum)), (int)Columns);
+    // Allow for up to 5 bytes per character.
+    s = vim_strnsave(skipwhite(ml_get(mp->lnum)), (int)Columns * 5);
     if (s == NULL)
 	return NULL;
-    /* Truncate the line to fit it in the window */
+    // Truncate the line to fit it in the window.
     len = 0;
     for (p = s; *p != NUL; MB_PTR_ADV(p))
     {