diff --git a/cocoa/me/dupeguru.xcodeproj/project.pbxproj b/cocoa/me/dupeguru.xcodeproj/project.pbxproj
index 2a52805f..4fd1c67e 100644
--- a/cocoa/me/dupeguru.xcodeproj/project.pbxproj
+++ b/cocoa/me/dupeguru.xcodeproj/project.pbxproj
@@ -963,7 +963,6 @@
 		C01FCF4C08A954540054247B /* release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
 				DEPLOYMENT_LOCATION = YES;
 				DEPLOYMENT_POSTPROCESSING = YES;
 				DSTROOT = /;
@@ -1006,7 +1005,6 @@
 		CED596C6111AF56D00C0CF2B /* dev */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
 				DEPLOYMENT_LOCATION = YES;
 				DEPLOYMENT_POSTPROCESSING = YES;
 				DSTROOT = /;
diff --git a/cocoa/pe/dupeguru.xcodeproj/project.pbxproj b/cocoa/pe/dupeguru.xcodeproj/project.pbxproj
index 87c55dbb..d9547371 100644
--- a/cocoa/pe/dupeguru.xcodeproj/project.pbxproj
+++ b/cocoa/pe/dupeguru.xcodeproj/project.pbxproj
@@ -968,7 +968,6 @@
 		C01FCF4C08A954540054247B /* release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
 				DEPLOYMENT_LOCATION = YES;
 				DEPLOYMENT_POSTPROCESSING = YES;
 				DSTROOT = /;
@@ -1011,7 +1010,6 @@
 		CEE00FF1111AF37400BC1A77 /* dev */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
 				DEPLOYMENT_LOCATION = YES;
 				DEPLOYMENT_POSTPROCESSING = YES;
 				DSTROOT = /;
diff --git a/cocoa/se/dupeguru.xcodeproj/project.pbxproj b/cocoa/se/dupeguru.xcodeproj/project.pbxproj
index 5ed55050..76c8b33a 100644
--- a/cocoa/se/dupeguru.xcodeproj/project.pbxproj
+++ b/cocoa/se/dupeguru.xcodeproj/project.pbxproj
@@ -947,7 +947,6 @@
 		C01FCF4C08A954540054247B /* release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
 				DEPLOYMENT_LOCATION = YES;
 				DEPLOYMENT_POSTPROCESSING = YES;
 				DSTROOT = /;
@@ -986,7 +985,6 @@
 		CE85E850111AF63D00187B0D /* dev */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
 				DEPLOYMENT_LOCATION = YES;
 				DEPLOYMENT_POSTPROCESSING = YES;
 				DSTROOT = /;
diff --git a/package.py b/package.py
index 9855c307..b0b8ef12 100644
--- a/package.py
+++ b/package.py
@@ -6,23 +6,38 @@
 # which should be included with this package. The terms are also available at 
 # http://www.hardcoded.net/licenses/bsd_license
 
-import sys
 import os
 import os.path as op
 import compileall
 import shutil
 import json
+from argparse import ArgumentParser
 
 from hscommon.plat import ISWINDOWS, ISLINUX
 from hscommon.build import (build_dmg, add_to_pythonpath, print_and_do, copy_packages,
     build_debian_changelog, copy_qt_plugins, get_module_version)
 
-def package_cocoa(edition):
+def parse_args():
+    parser = ArgumentParser()
+    parser.add_argument('--sign', dest='sign_identity',
+        help="Sign app under specified identity before packaging (OS X only)")
+    args = parser.parse_args()
+    return args
+
+def package_cocoa(edition, sign_identity):
     app_path = {
         'se': 'cocoa/se/dupeGuru.app',
         'me': 'cocoa/me/dupeGuru ME.app',
         'pe': 'cocoa/pe/dupeGuru PE.app',
     }[edition]
+    # Rather than signing our app in XCode during the build phase, we sign it during the package
+    # phase because running the app before packaging can modify it and we want to be sure to have
+    # a valid signature.
+    if sign_identity:
+        sign_identity = "Developer ID Application: {}".format(sign_identity)
+        print_and_do('codesign --force --sign "{}" "{}"'.format(sign_identity, app_path))
+    else:
+        print("WARNING: packaging an unsigned application")
     build_dmg(app_path, '.')
 
 def package_windows(edition, dev):
@@ -107,13 +122,14 @@ def package_debian(edition):
     os.system("dpkg-buildpackage")
 
 def main():
+    args = parse_args()
     conf = json.load(open('conf.json'))
     edition = conf['edition']
     ui = conf['ui']
     dev = conf['dev']
     print("Packaging dupeGuru {0} with UI {1}".format(edition.upper(), ui))
     if ui == 'cocoa':
-        package_cocoa(edition)
+        package_cocoa(edition, args.sign_identity)
     elif ui == 'qt':
         if ISWINDOWS:
             package_windows(edition, dev)