diff --git a/Gruntfile.js b/Gruntfile.js
index f3af756..92fea4b 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -129,6 +129,17 @@ module.exports = function(grunt) {
       files: {
         src: '_site/**/*.html'
       }
+    },
+
+    sed: {
+      versionNumber: {
+        pattern: (function () {
+          var old = grunt.option('oldver');
+          return old ? RegExp.quote(old) : old;
+        })(),
+        replacement: grunt.option('newver'),
+        recursive: true
+      }
     }
   });
 
@@ -142,4 +153,9 @@ module.exports = function(grunt) {
   grunt.registerTask('validate-html', ['jekyll', 'validation']);
   grunt.registerTask('default', ['dist']);
   grunt.registerTask('build', ['dist']);
+
+  // Version numbering task.
+  // grunt change-version-number --oldver=A.B.C --newver=X.Y.Z
+  // This can be overzealous, so its changes should always be manually reviewed!
+  grunt.registerTask('change-version-number', 'sed');
 };
diff --git a/package.json b/package.json
index a039263..9a99b01 100644
--- a/package.json
+++ b/package.json
@@ -32,6 +32,7 @@
     "grunt-contrib-watch": "~0.5.3",
     "grunt-html-validation": "~0.1.13",
     "grunt-jekyll": "~0.4.1",
+    "grunt-sed": "~0.1.1",
     "load-grunt-tasks": "~0.4.0"
   }
 }