diff --git a/lib/codemirror.js b/lib/codemirror.js
index 7a4e2550ea16dc6e76f3b84d036c038260c7626a..00029878274c95485005d471703d214e730f83bd 100644
--- a/lib/codemirror.js
+++ b/lib/codemirror.js
@@ -1025,6 +1025,7 @@ window.CodeMirror = (function() {
     cm.display.measureLineCache.length = cm.display.measureLineCachePos = 0;
     cm.display.cachedCharWidth = cm.display.cachedTextHeight = null;
     cm.display.maxLineChanged = true;
+    cm.display.lineNumChars = null;
   }
 
   // Context is one of "line", "div" (display.lineDiv), "local"/null (editor), or "page"