Index: src/fossil.diff.js
==================================================================
--- src/fossil.diff.js
+++ src/fossil.diff.js
@@ -669,12 +669,14 @@
       e.style.maxWidth = w + "px";
     });
     if(force || !f.colsU){
       f.colsU = document.querySelectorAll('td.difftxtu pre');
     }
-    w = lastWidth - 100;
     f.colsU.forEach(function(e){
+      w = lastWidth - 3; // Outer border
+      var k = e.parentElement/*TD*/;
+      while(k = k.previousElementSibling/*TD*/) w -= k.scrollWidth;
       e.style.width = w + "px";
       e.style.maxWidth = w + "px";
     });
     if(0){ // seems to be unnecessary
       if(!f.allDiffs){