diff --git a/package.json b/package.json
index 82f80b3..a1cd4db 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
   "scripts": {
     "clean": "rimraf ./dist ./static/assets",
     "start": "mkdirp ./dist && electron-webpack dev --bail --display-error-details --env.minify=false",
+    "postinstall": "npm run rebuild-deps",
     "compile": "mkdirp ./dist && electron-webpack --bail --display-error-details --env.minify=false",
     "fetch": "rimraf ./static/assets/ && mkdirp ./static/assets/ && node ./scripts/fetchMediaLibraryAssets.js",
     "build": "npm run build:dev",
diff --git a/scripts/rebuild-deps.js b/scripts/rebuild-deps.js
index d29422b..1001baa 100644
--- a/scripts/rebuild-deps.js
+++ b/scripts/rebuild-deps.js
@@ -2,8 +2,13 @@ const fs = require('fs');
 
 const desktopPackage = require('../package.json');
 const desktopRawPackage = require('../package-deps.json');
-const guiPackage = require('../node_modules/scratch-gui/package.json');
+const guiPackage = require('scratch-gui/package.json');
 
+/**
+ * Sort an object's keys.
+ * @param {object} obj - the object whose keys should be sorted.
+ * @returns {object} - a new object with the same keys and values, but the keys are sorted by {@link Array#sort}.
+ */
 const sortObject = obj => Object
     .keys(obj)
     .sort()
@@ -15,12 +20,51 @@ const sortObject = obj => Object
         {}
     );
 
-desktopPackage.devDependencies = sortObject(Object.assign(
-    {},
-    guiPackage.devDependencies,
-    desktopRawPackage.devDependencies
-));
+/**
+ * Make a shallow comparison of two objects, returning true if they match. This shallow comparison returns true iff:
+ * - the two objects have the same number of keys, AND
+ * - each key of obj1 is present in obj2 (via hasOwnProperty), AND
+ * - the value associated with each key in obj1 matches (using ===) the value associated with the same key in obj2
+ * Note that the order of keys is not compared.
+ * @param {object} obj1 - the first object to compare
+ * @param {object} obj2 - the second object to compare
+ * @returns {boolean} - true if the objects are shallow-identical.
+ */
+const shallowCompare = (obj1, obj2) =>
+    Object.keys(obj1).length === Object.keys(obj2).length &&
+    Object.keys(obj1).every(k => Object.prototype.hasOwnProperty.call(obj2, k) && (obj1[k] === obj2[k]));
 
-let newDesktopPackage = JSON.stringify(desktopPackage, null, 2);
-newDesktopPackage += '\n';
-fs.writeFileSync('package.json', newDesktopPackage);
+/**
+ * Merge `scratch-gui` and `scratch-desktop` dependencies:
+ * 1. Merge the dependencies found in `scratch-gui/package.json` with those in `package-deps.json`.
+ * 2. Report statistics.
+ * 3. If the result differs from `package.json`, rewrite `package.json` with the new dependencies and print a warning.
+ */
+const rebuildDeps = () => {
+    const oldDevDependencies = desktopPackage.devDependencies;
+    desktopPackage.devDependencies = sortObject(Object.assign(
+        {},
+        guiPackage.devDependencies,
+        desktopRawPackage.devDependencies
+    ));
+
+    console.log(`Direct dependencies (desktop / gui / merged): ${
+        Object.keys(desktopRawPackage.devDependencies).length} / ${
+        Object.keys(guiPackage.devDependencies).length} / ${
+        Object.keys(desktopPackage.devDependencies).length}`);
+    if (shallowCompare(oldDevDependencies, desktopPackage.devDependencies)) {
+        console.log('Dependencies in package.json were already up-to-date.');
+    } else {
+        let newDesktopPackage = JSON.stringify(desktopPackage, null, 2);
+        newDesktopPackage += '\n';
+        fs.writeFileSync('package.json', newDesktopPackage);
+        console.warn(
+            '\n', // NPM adds a prefix to all BUT the first line, so this makes the remaining lines format correctly
+            '***\n',
+            '*** Dependencies in package.json have been updated! Please re-run npm to install these updates.\n',
+            '***\n'
+        );
+    }
+};
+
+rebuildDeps();