diff --git a/testing/mozharness/configs/builds/releng_base_mac_64_builds.py b/testing/mozharness/configs/builds/releng_base_mac_64_builds.py
index 777c02bd22d9..6309d1e54e48 100644
--- a/testing/mozharness/configs/builds/releng_base_mac_64_builds.py
+++ b/testing/mozharness/configs/builds/releng_base_mac_64_builds.py
@@ -19,6 +19,7 @@ config = {
     ],
     "buildbot_json_path": "buildprops.json",
     'exes': {
+        'python2.7': sys.executable,
         "buildbot": "/tools/buildbot/bin/buildbot",
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
diff --git a/testing/mozharness/configs/builds/releng_base_mac_64_cross_builds.py b/testing/mozharness/configs/builds/releng_base_mac_64_cross_builds.py
index aa68d3850633..2adf4646eb07 100644
--- a/testing/mozharness/configs/builds/releng_base_mac_64_cross_builds.py
+++ b/testing/mozharness/configs/builds/releng_base_mac_64_cross_builds.py
@@ -16,6 +16,7 @@ config = {
     ],
     "buildbot_json_path": "buildprops.json",
     'exes': {
+        'python2.7': sys.executable,
         "buildbot": "/tools/buildbot/bin/buildbot",
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
diff --git a/testing/mozharness/configs/builds/releng_base_windows_32_builds.py b/testing/mozharness/configs/builds/releng_base_windows_32_builds.py
index 8735f9a7cad0..ab56666f6a81 100644
--- a/testing/mozharness/configs/builds/releng_base_windows_32_builds.py
+++ b/testing/mozharness/configs/builds/releng_base_windows_32_builds.py
@@ -23,6 +23,7 @@ config = {
     ],
     "buildbot_json_path": "buildprops.json",
     'exes': {
+        'python2.7': sys.executable,
         "buildbot": [
             sys.executable,
             'c:\\mozilla-build\\buildbotve\\scripts\\buildbot'
diff --git a/testing/mozharness/configs/builds/releng_base_windows_64_builds.py b/testing/mozharness/configs/builds/releng_base_windows_64_builds.py
index cb30e0b11e07..47d0fc1d4de9 100644
--- a/testing/mozharness/configs/builds/releng_base_windows_64_builds.py
+++ b/testing/mozharness/configs/builds/releng_base_windows_64_builds.py
@@ -23,6 +23,7 @@ config = {
     ],
     "buildbot_json_path": "buildprops.json",
     'exes': {
+        'python2.7': sys.executable,
         "buildbot": [
             sys.executable,
             'c:\\mozilla-build\\buildbotve\\scripts\\buildbot'
diff --git a/testing/mozharness/configs/builds/releng_sub_mac_configs/64_artifact.py b/testing/mozharness/configs/builds/releng_sub_mac_configs/64_artifact.py
index f619386c14f7..1f094748c5b7 100644
--- a/testing/mozharness/configs/builds/releng_sub_mac_configs/64_artifact.py
+++ b/testing/mozharness/configs/builds/releng_sub_mac_configs/64_artifact.py
@@ -15,6 +15,7 @@ config = {
     ],
     "buildbot_json_path": "buildprops.json",
     'exes': {
+        'python2.7': sys.executable,
         "buildbot": "/tools/buildbot/bin/buildbot",
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
diff --git a/testing/mozharness/configs/builds/releng_sub_mac_configs/64_debug_artifact.py b/testing/mozharness/configs/builds/releng_sub_mac_configs/64_debug_artifact.py
index 041ef491ba48..ae01b1575c0c 100644
--- a/testing/mozharness/configs/builds/releng_sub_mac_configs/64_debug_artifact.py
+++ b/testing/mozharness/configs/builds/releng_sub_mac_configs/64_debug_artifact.py
@@ -17,6 +17,7 @@ config = {
     ],
     "buildbot_json_path": "buildprops.json",
     'exes': {
+        'python2.7': sys.executable,
         "buildbot": "/tools/buildbot/bin/buildbot",
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang.py b/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang.py
index 06b2ff08e326..3c71730cf0ae 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang.py
@@ -22,6 +22,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang_debug.py
index 95cfc7186245..e2a6ff934058 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang_debug.py
@@ -22,6 +22,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_debug.py
index 42d390854fb4..53a26a1670e5 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_debug.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_opt.py b/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_opt.py
index 51aff5a37b3e..c02fa0eacd2b 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_opt.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_debug.py
index 5e8d974f3382..9664a8b8f51f 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_debug.py
@@ -22,6 +22,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_opt.py b/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_opt.py
index 8702bed13fa4..c57451500c6f 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_opt.py
@@ -22,6 +22,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang.py b/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang.py
index 8e1950eaf2cc..11740deae8c4 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang.py
@@ -22,6 +22,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang_debug.py
index 6c9d8ae24fc2..a12155f0d7aa 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang_debug.py
@@ -22,6 +22,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_debug.py
index dcd0bb4fe8ea..94472e05749d 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_debug.py
@@ -18,6 +18,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_opt.py b/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_opt.py
index 1b331a5bf95a..c056176a65df 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_opt.py
@@ -18,6 +18,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_addondevel.py b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_addondevel.py
index 2409d966c3cb..cc3b3af011ab 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_addondevel.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_addondevel.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_debug.py
index 0ac94f57e683..c2820ed083c2 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_debug.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_opt.py b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_opt.py
index c1bcd37f5ab7..73399348f2da 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_opt.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_addondevel.py b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_addondevel.py
index e84374b205b3..c4fc7ae4462a 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_addondevel.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_addondevel.py
@@ -24,6 +24,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_debug.py b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_debug.py
index 868af9176bdc..a36abf812c96 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_debug.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_opt.py b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_opt.py
index 8e2fc27887ca..b79a4576182d 100644
--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_opt.py
@@ -23,6 +23,7 @@ config = {
         'check-test',
     ],
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
diff --git a/testing/mozharness/configs/single_locale/win32.py b/testing/mozharness/configs/single_locale/win32.py
index f6780ec1b3f7..a4dd185e86fe 100644
--- a/testing/mozharness/configs/single_locale/win32.py
+++ b/testing/mozharness/configs/single_locale/win32.py
@@ -68,6 +68,7 @@ config = {
     # use mozmake?
     "enable_mozmake": True,
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             'c:/mozilla-build/buildbotve/virtualenv.py'
diff --git a/testing/mozharness/configs/single_locale/win64.py b/testing/mozharness/configs/single_locale/win64.py
index 6a859e8c7279..fcc51e2bb1f0 100644
--- a/testing/mozharness/configs/single_locale/win64.py
+++ b/testing/mozharness/configs/single_locale/win64.py
@@ -68,6 +68,7 @@ config = {
     # use mozmake?
     "enable_mozmake": True,
     'exes': {
+        'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             'c:/mozilla-build/buildbotve/virtualenv.py'
diff --git a/testing/mozharness/mozharness/mozilla/building/buildbase.py b/testing/mozharness/mozharness/mozilla/building/buildbase.py
index 5253d279cd14..67897ae1272f 100755
--- a/testing/mozharness/mozharness/mozilla/building/buildbase.py
+++ b/testing/mozharness/mozharness/mozilla/building/buildbase.py
@@ -750,8 +750,9 @@ or run without that action (ie: --no-{action})"
             app_ini_path = dirs['abs_app_ini_path']
         if (os.path.exists(print_conf_setting_path) and
                 os.path.exists(app_ini_path)):
+            python = self.query_exe('python2.7')
             cmd = [
-                sys.executable, os.path.join(dirs['abs_src_dir'], 'mach'), 'python',
+                python, os.path.join(dirs['abs_src_dir'], 'mach'), 'python',
                 print_conf_setting_path, app_ini_path,
                 'App', prop
             ]
@@ -1304,8 +1305,9 @@ or run without that action (ie: --no-{action})"
                                             dirs['abs_app_ini_path']),
                      level=error_level)
         self.info("Setting properties found in: %s" % dirs['abs_app_ini_path'])
+        python = self.query_exe('python2.7')
         base_cmd = [
-            sys.executable, os.path.join(dirs['abs_src_dir'], 'mach'), 'python',
+            python, os.path.join(dirs['abs_src_dir'], 'mach'), 'python',
             print_conf_setting_path, dirs['abs_app_ini_path'], 'App'
         ]
         properties_needed = [
@@ -1642,7 +1644,7 @@ or run without that action (ie: --no-{action})"
                 os.path.join(dirs['abs_src_dir'], 'mach')
             ]
         else:
-            mach = [sys.executable, 'mach']
+            mach = [self.query_exe('python2.7'), 'mach']
 
         return_code = self.run_command_m(
             command=mach + ['--log-no-times', 'build', '-v'],
@@ -1766,8 +1768,9 @@ or run without that action (ie: --no-{action})"
     def _execute_postflight_build_mach_command(self, mach_command_args):
         env = self.query_build_env()
         env.update(self.query_mach_build_env())
+        python = self.query_exe('python2.7')
 
-        command = [sys.executable, 'mach', '--log-no-times']
+        command = [python, 'mach', '--log-no-times']
         command.extend(mach_command_args)
 
         self.run_command_m(
@@ -1784,10 +1787,11 @@ or run without that action (ie: --no-{action})"
         """generates source archives and uploads them"""
         env = self.query_build_env()
         env.update(self.query_mach_build_env())
+        python = self.query_exe('python2.7')
         dirs = self.query_abs_dirs()
 
         self.run_command_m(
-            command=[sys.executable, 'mach', '--log-no-times', 'configure'],
+            command=[python, 'mach', '--log-no-times', 'configure'],
             cwd=dirs['abs_src_dir'],
             env=env, output_timeout=60*3, halt_on_failure=True,
         )
@@ -1839,8 +1843,9 @@ or run without that action (ie: --no-{action})"
         env = self.query_build_env()
         env.update(self.query_check_test_env())
 
+        python = self.query_exe('python2.7')
         cmd = [
-            sys.executable, 'mach',
+            python, 'mach',
             '--log-no-times',
             'build',
             '-v',
@@ -2211,8 +2216,9 @@ or run without that action (ie: --no-{action})"
         env = self.query_build_env()
         env.update(self.query_mach_build_env())
 
+        python = self.query_exe('python2.7')
         return_code = self.run_command_m(
-            command=[sys.executable, 'mach', 'valgrind-test'],
+            command=[python, 'mach', 'valgrind-test'],
             cwd=self.query_abs_dirs()['abs_src_dir'],
             env=env, output_timeout=self.config.get('max_build_output_timeout', 60 * 40)
         )
diff --git a/testing/mozharness/mozharness/mozilla/l10n/locales.py b/testing/mozharness/mozharness/mozilla/l10n/locales.py
index 23f4794470bf..4812fd41966a 100755
--- a/testing/mozharness/mozharness/mozilla/l10n/locales.py
+++ b/testing/mozharness/mozharness/mozilla/l10n/locales.py
@@ -146,10 +146,11 @@ class LocalesMixin(ChunkingMixin):
     def run_compare_locales(self, locale, halt_on_failure=False):
         dirs = self.query_abs_dirs()
         env = self.query_l10n_env()
+        python = self.query_exe('python2.7')
         compare_locales_error_list = list(PythonErrorList)
         self.rmtree(dirs['abs_merge_dir'])
         self.mkdir_p(dirs['abs_merge_dir'])
-        command = [sys.executable, 'mach', 'compare-locales',
+        command = [python, 'mach', 'compare-locales',
                    '--merge-dir', dirs['abs_merge_dir'],
                    '--l10n-ini', os.path.join(dirs['abs_locales_src_dir'], 'l10n.ini'),
                    '--l10n-base', dirs['abs_l10n_dir'], locale]
diff --git a/testing/mozharness/scripts/desktop_l10n.py b/testing/mozharness/scripts/desktop_l10n.py
index 1cafe4f50f57..44218a27d1c3 100755
--- a/testing/mozharness/scripts/desktop_l10n.py
+++ b/testing/mozharness/scripts/desktop_l10n.py
@@ -698,7 +698,8 @@ class DesktopSingleLocale(LocalesMixin, ReleaseMixin, MockMixin, BuildbotMixin,
         return self._mach(target=target, env=env)
 
     def _get_mach_executable(self):
-        return [sys.executable, 'mach']
+        python = self.query_exe('python2.7')
+        return [python, 'mach']
 
     def _get_make_executable(self):
         config = self.config
diff --git a/testing/mozharness/scripts/desktop_partner_repacks.py b/testing/mozharness/scripts/desktop_partner_repacks.py
index 5064117d0c1b..ff07dffc8438 100755
--- a/testing/mozharness/scripts/desktop_partner_repacks.py
+++ b/testing/mozharness/scripts/desktop_partner_repacks.py
@@ -172,7 +172,8 @@ class DesktopPartnerRepacks(ReleaseMixin, BuildbotMixin, PurgeMixin,
 
     def repack(self):
         """creates the repacks"""
-        repack_cmd = [sys.executable, "partner-repacks.py",
+        python = self.query_exe("python2.7")
+        repack_cmd = [python, "partner-repacks.py",
                       "-v", self.config['version'],
                       "-n", str(self.config['build_number'])]
         if self.config.get('platform'):
diff --git a/testing/mozharness/scripts/repackage.py b/testing/mozharness/scripts/repackage.py
index bde89ae5f669..a9c6d2b53fb8 100644
--- a/testing/mozharness/scripts/repackage.py
+++ b/testing/mozharness/scripts/repackage.py
@@ -78,9 +78,10 @@ class Repackage(BaseScript):
     def repackage(self):
         config = self.config
         dirs = self.query_abs_dirs()
+        python = self.query_exe('python2.7')
         infile = os.path.join(config['input_home'], config['input_filename'])
         outfile = os.path.join(dirs['abs_upload_dir'], config['output_filename'])
-        command = [sys.executable, 'mach', '--log-no-times', 'repackage',
+        command = [python, 'mach', '--log-no-times', 'repackage',
                    '--input', infile,
                    '--output', outfile]
         return self.run_command(
@@ -134,7 +135,8 @@ class Repackage(BaseScript):
 
     def _run_configure(self):
         dirs = self.query_abs_dirs()
-        command = [sys.executable, 'mach', '--log-no-times', 'configure']
+        python = self.query_exe('python2.7')
+        command = [python, 'mach', '--log-no-times', 'configure']
         return self.run_command(
             command=command,
             cwd=dirs['abs_mozilla_dir'],