diff --git a/Gulpfile.js b/Gulpfile.js
index 52744e12740..db7bb76d34b 100644
--- a/Gulpfile.js
+++ b/Gulpfile.js
@@ -12,6 +12,7 @@ const clone = require("gulp-clone");
 const newer = require("gulp-newer");
 const tsc = require("gulp-typescript");
 const tsc_oop = require("./scripts/build/gulp-typescript-oop");
+const getDirSize = require("./scripts/build/getDirSize");
 const insert = require("gulp-insert");
 const sourcemaps = require("gulp-sourcemaps");
 const Q = require("q");
@@ -588,7 +589,13 @@ gulp.task("VerifyLKG", /*help*/ false, [], () => {
 gulp.task("LKGInternal", /*help*/ false, ["lib", "local"]);
 
 gulp.task("LKG", "Makes a new LKG out of the built js files", ["clean", "dontUseDebugMode"], () => {
-    return runSequence("LKGInternal", "VerifyLKG");
+    const sizeBefore = getDirSize(lkgDirectory);
+    const seq = runSequence("LKGInternal", "VerifyLKG");
+    const sizeAfter = getDirSize(lkgDirectory);
+    if (sizeAfter > (sizeBefore * 1.10)) {
+        throw new Error("The lib folder increased by 10% or more. This likely indicates a bug.");
+    }
+    return seq;
 });
 
 
diff --git a/Jakefile.js b/Jakefile.js
index 55729eecaad..a6483355c73 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -8,6 +8,7 @@ var path = require("path");
 var child_process = require("child_process");
 var fold = require("travis-fold");
 var ts = require("./lib/typescript");
+const getDirSize = require("./scripts/build/getDirSize");
 
 // Variables
 var compilerDirectory = "src/compiler/";
@@ -642,26 +643,24 @@ task("generate-spec", [specMd]);
 
 // Makes a new LKG. This target does not build anything, but errors if not all the outputs are present in the built/local directory
 desc("Makes a new LKG out of the built js files");
-task("LKG", ["clean", "release", "local"].concat(libraryTargets), function () {
+task("LKG", ["clean", "release", "local"].concat(libraryTargets), () => {
+    const sizeBefore = getDirSize(LKGDirectory);
     var expectedFiles = [tscFile, servicesFile, serverFile, nodePackageFile, nodeDefinitionsFile, standaloneDefinitionsFile, tsserverLibraryFile, tsserverLibraryDefinitionFile, cancellationTokenFile, typingsInstallerFile, buildProtocolDts, watchGuardFile].
         concat(libraryTargets).
         concat(localizationTargets);
-    var missingFiles = expectedFiles.filter(function (f) {
-        return !fs.existsSync(f);
-    });
+    var missingFiles = expectedFiles.filter(f => !fs.existsSync(f));
     if (missingFiles.length > 0) {
         fail(new Error("Cannot replace the LKG unless all built targets are present in directory " + builtLocalDirectory +
             ". The following files are missing:\n" + missingFiles.join("\n")));
     }
     // Copy all the targets into the LKG directory
     jake.mkdirP(LKGDirectory);
-    for (i in expectedFiles) {
-        jake.cpR(expectedFiles[i], LKGDirectory);
+    expectedFiles.forEach(f => jake.cpR(f, LKGDirectory));
+
+    const sizeAfter = getDirSize(LKGDirectory);
+    if (sizeAfter > (sizeBefore * 1.10)) {
+        throw new Error("The lib folder increased by 10% or more. This likely indicates a bug.");
     }
-    //var resourceDirectories = fs.readdirSync(builtLocalResourcesDirectory).map(function(p) { return path.join(builtLocalResourcesDirectory, p); });
-    //resourceDirectories.map(function(d) {
-    //    jake.cpR(d, LKGResourcesDirectory);
-    //});
 });
 
 // Test directory
diff --git a/scripts/build/getDirSize.js b/scripts/build/getDirSize.js
new file mode 100644
index 00000000000..278c4e7f009
--- /dev/null
+++ b/scripts/build/getDirSize.js
@@ -0,0 +1,30 @@
+// @ts-check
+const { lstatSync, readdirSync } = require("fs");
+const { join } = require("path");
+
+/**
+ * Find the size of a directory recursively.
+ * Symbolic links are counted once (same inode).
+ * @param {string} root
+ * @param {Set} seen
+ * @returns {number} bytes
+ */
+function getDirSize(root, seen = new Set()) {
+    const stats = lstatSync(root);
+
+    if (seen.has(stats.ino)) {
+        return 0;
+    }
+
+    seen.add(stats.ino);
+
+    if (!stats.isDirectory()) {
+        return stats.size;
+    }
+
+    return readdirSync(root)
+        .map(file => getDirSize(join(root, file), seen))
+        .reduce((acc, num) => acc + num, 0);
+}
+
+module.exports = getDirSize;