diff --git a/src/winio.c b/src/winio.c
index 8b3a8e99..8da48eba 100644
--- a/src/winio.c
+++ b/src/winio.c
@@ -2328,7 +2328,7 @@ char *display_string(const char *buf, size_t start_col, size_t len, bool
     assert(column <= start_col);
 
     /* Allocate enough space for the entire line. */
-    alloc_len = (mb_cur_max() * COLS);
+    alloc_len = (mb_cur_max() * (COLS + 1));
 
     converted = charalloc(alloc_len + 1);
     index = 0;