diff --git a/src/browser/main.coffee b/src/browser/main.coffee
index 989ef537b..ce362839e 100644
--- a/src/browser/main.coffee
+++ b/src/browser/main.coffee
@@ -80,7 +80,7 @@ parseCommandLine = ->
     opened or a new window if it hasn't.
   """
   options.alias('d', 'dev').boolean('d').describe('d', 'Run in development mode.')
-  options.alias('r', 'resource-path').string('r').describe('r', 'Set the path from which Atom loads internal resources and enable dev-mode.')
+  options.alias('r', 'resource-path').string('r').describe('r', 'Set the path to the Atom source directory and enable dev-mode.')
   options.alias('f', 'foreground').boolean('f').describe('f', 'Keep the browser process in the foreground.')
   options.alias('h', 'help').boolean('h').describe('h', 'Print this usage message.')
   options.alias('l', 'log-file').string('l').describe('l', 'Log all output to file.')
@@ -114,8 +114,18 @@ parseCommandLine = ->
   if args['resource-path']
     devMode = true
     resourcePath = args['resource-path']
-  else if devMode
-    resourcePath = global.devResourcePath
+  else
+    # Set resourcePath based on to specDirectory if running specs on atom core
+    if specDirectory?
+      packageDirectoryPath = path.join(specDirectory, '..')
+      packageManifestPath = path.join(packageDirectoryPath, 'package.json')
+      if fs.statSyncNoException(packageManifestPath)
+        try
+          packageManifest = JSON.parse(fs.readFileSync(packageManifestPath, 'utf8'))
+          resourcePath = packageDirectoryPath if packageManifest.name is 'atom'
+
+    if devMode
+      resourcePath ?= global.devResourcePath
 
   unless fs.statSyncNoException(resourcePath)
     resourcePath = path.dirname(path.dirname(__dirname))