diff --git a/tools/compiler.js b/tools/compiler.js
index c9266520e8..a498251334 100644
--- a/tools/compiler.js
+++ b/tools/compiler.js
@@ -45,6 +45,9 @@ compiler.compile = function (packageSource, options) {
         "` in package `" + packageSource.name + "`",
       rootPath: packageSource.sourceRoot
     }, function () {
+      // XXX we should probably also pass options.noLineNumbers into
+      //     buildJsImage so it can pass it back to its call to
+      //     compiler.compile
       var buildResult = bundler.buildJsImage({
         name: info.name,
         packageMap: packageMap,
@@ -125,7 +128,8 @@ compiler.compile = function (packageSource, options) {
       sourceArch: unibuild,
       isopackCache: isopackCache,
       nodeModulesPath: nodeModulesPath,
-      isPortable: isPortable
+      isPortable: isPortable,
+      noLineNumbers: options.noLineNumbers
     });
     _.extend(pluginProviderPackageNames,
              unibuildResult.pluginProviderPackageNames);
@@ -150,6 +154,7 @@ var compileUnibuild = function (options) {
   var isopackCache = options.isopackCache;
   var nodeModulesPath = options.nodeModulesPath;
   var isPortable = options.isPortable;
+  var noLineNumbers = options.noLineNumbers;
 
   var isApp = ! inputSourceArch.pkg.name;
   var resources = [];
@@ -738,7 +743,8 @@ var compileUnibuild = function (options) {
       (inputSourceArch.kind === "main" ? "" : (":" + inputSourceArch.kind)) + ".js",
     name: inputSourceArch.pkg.name || null,
     declaredExports: _.pluck(inputSourceArch.declaredExports, 'name'),
-    jsAnalyze: jsAnalyze
+    jsAnalyze: jsAnalyze,
+    noLineNumbers: noLineNumbers
   });
 
   // *** Determine captured variables
diff --git a/tools/isopack-cache.js b/tools/isopack-cache.js
index ad60f9f19d..eba846f071 100644
--- a/tools/isopack-cache.js
+++ b/tools/isopack-cache.js
@@ -36,6 +36,8 @@ exports.IsopackCache = function (options) {
   // tropohouse, and otherwise is a PackageMap object listing
   self._isopacks = {};
 
+  self._noLineNumbers = !! options.noLineNumbers;
+
   self.allLoadedLocalPackagesWatchSet = new watch.WatchSet;
 };
 
@@ -204,7 +206,8 @@ _.extend(exports.IsopackCache.prototype, {
         // Nope! Compile it again.
         var compilerResult = compiler.compile(packageInfo.packageSource, {
           packageMap: self._packageMap,
-          isopackCache: self
+          isopackCache: self,
+          noLineNumbers: self._noLineNumbers
         });
         // Accept the compiler's result, even if there were errors (since it at
         // least will have a useful WatchSet and will allow us to keep going and
diff --git a/tools/isopackets.js b/tools/isopackets.js
index 719317be68..1d24792573 100644
--- a/tools/isopackets.js
+++ b/tools/isopackets.js
@@ -236,7 +236,13 @@ var makeIsopacketBuildContext = function () {
   // Make an isopack cache that doesn't save isopacks to disk and has no
   // access to versioned packages.
   context.isopackCache = new isopackCacheModule.IsopackCache({
-    packageMap: context.packageMap
+    packageMap: context.packageMap,
+    // When linking JS files, don't include the padding spaces and line number
+    // comments. Since isopackets are loaded as part of possibly very short
+    // 'meteor' tool command invocations, we care more about startup time than
+    // legibility, and the difference is actually observable (eg 25% speedup
+    // loading constraint-solver).
+    noLineNumbers: true
   });
   return context;
 };
diff --git a/tools/linker.js b/tools/linker.js
index eb895f147e..2923fd1ba0 100644
--- a/tools/linker.js
+++ b/tools/linker.js
@@ -32,6 +32,7 @@ var Module = function (options) {
   self.combinedServePath = options.combinedServePath;
   self.importStubServePath = options.importStubServePath;
   self.jsAnalyze = options.jsAnalyze;
+  self.noLineNumbers = options.noLineNumbers;
 };
 
 _.extend(Module.prototype, {
@@ -134,7 +135,10 @@ _.extend(Module.prototype, {
     _.each(self.files, function (file) {
       if (!_.isEmpty(chunks))
         chunks.push("\n\n\n\n\n\n");
-      chunks.push(file.getPrelinkedOutput({ sourceWidth: sourceWidth }));
+      chunks.push(file.getPrelinkedOutput({
+        sourceWidth: sourceWidth,
+        noLineNumbers: self.noLineNumbers
+      }));
     });
 
     var node = new sourcemap.SourceNode(null, null, null, chunks);
@@ -291,6 +295,8 @@ _.extend(File.prototype, {
   // - preserveLineNumbers: if true, decorate minimally so that line
   //   numbers don't change between input and output. In this case,
   //   sourceWidth is ignored.
+  // - noLineNumbers: We still include the banners and such, but
+  //   no line number suffix.
   // - sourceWidth: width in columns to use for the source code
   //
   // Returns a SourceNode.
@@ -355,7 +361,8 @@ _.extend(File.prototype, {
       _.each(lines, function (line) {
         var suffix = "\n";
 
-        if (line.length <= width && line[line.length - 1] !== "\\") {
+        if (! options.noLineNumbers
+            && line.length <= width && line[line.length - 1] !== "\\") {
           suffix = padding.slice(line.length, width) + " // " + num + "\n";
         }
         f(line, suffix, num);
@@ -494,7 +501,8 @@ var prelink = function (options) {
     useGlobalNamespace: options.useGlobalNamespace,
     importStubServePath: options.importStubServePath,
     combinedServePath: options.combinedServePath,
-    jsAnalyze: options.jsAnalyze
+    jsAnalyze: options.jsAnalyze,
+    noLineNumbers: options.noLineNumbers
   });
 
   _.each(options.inputFiles, function (inputFile) {