diff --git a/build/mach_initialize.py b/build/mach_initialize.py
index c47292f5739d..2c4669d0bbf6 100644
--- a/build/mach_initialize.py
+++ b/build/mach_initialize.py
@@ -260,11 +260,7 @@ def _activate_python_environment(topsrcdir, state_dir):
             # (optional) dependencies are not installed.
             _scrub_system_site_packages()
 
-        sys.path[0:0] = [
-            os.path.join(topsrcdir, pth.path)
-            for pth in requirements.pth_requirements
-            + requirements.vendored_requirements
-        ]
+        sys.path[0:0] = requirements.pths_as_absolute(topsrcdir)
     elif is_mach_virtualenv:
         # We're running in the Mach virtualenv - check that it's up-to-date.
         # Note that the "pip package check" exists to ensure that a virtualenv isn't
@@ -284,11 +280,7 @@ def _activate_python_environment(topsrcdir, state_dir):
         # Remove global site packages from sys.path to improve isolation accordingly.
         _scrub_system_site_packages()
 
-        sys.path[0:0] = [
-            os.path.join(topsrcdir, pth.path)
-            for pth in requirements.pth_requirements
-            + requirements.vendored_requirements
-        ]
+        sys.path[0:0] = requirements.pths_as_absolute(topsrcdir)
 
 
 def initialize(topsrcdir):
diff --git a/python/mach/mach/requirements.py b/python/mach/mach/requirements.py
index 2be2d5f1cd2d..adfab41451d7 100644
--- a/python/mach/mach/requirements.py
+++ b/python/mach/mach/requirements.py
@@ -82,6 +82,14 @@ class MachEnvRequirements:
         self.pypi_optional_requirements = []
         self.vendored_requirements = []
 
+    def pths_as_absolute(self, topsrcdir):
+        return sorted(
+            [
+                os.path.normcase(os.path.join(topsrcdir, pth.path))
+                for pth in (self.pth_requirements + self.vendored_requirements)
+            ]
+        )
+
     def validate_environment_packages(self, pip_command):
         result = EnvironmentPackageValidationResult()
         if not self.pypi_requirements and not self.pypi_optional_requirements:
diff --git a/python/mach/mach/virtualenv.py b/python/mach/mach/virtualenv.py
index 0ef14b98ec7d..8ad24a29a775 100644
--- a/python/mach/mach/virtualenv.py
+++ b/python/mach/mach/virtualenv.py
@@ -204,26 +204,11 @@ class VirtualenvManager(VirtualenvHelper):
                 with open(
                     os.path.join(self._site_packages_dir(), PTH_FILENAME)
                 ) as file:
-                    pth_lines = file.read().strip().split("\n")
+                    current_paths = file.read().strip().split("\n")
             except FileNotFoundError:
                 return False
 
-            current_paths = [
-                os.path.normcase(
-                    os.path.abspath(os.path.join(self._site_packages_dir(), path))
-                )
-                for path in pth_lines
-            ]
-
-            required_paths = [
-                os.path.normcase(
-                    os.path.abspath(os.path.join(self.topsrcdir, pth.path))
-                )
-                for pth in env_requirements.pth_requirements
-                + env_requirements.vendored_requirements
-            ]
-
-            if current_paths != required_paths:
+            if current_paths != env_requirements.pths_as_absolute(self.topsrcdir):
                 return False
 
         if not skip_pip_package_check:
@@ -310,17 +295,9 @@ class VirtualenvManager(VirtualenvHelper):
         self.create()
         env_requirements = self.requirements()
         site_packages_dir = self._site_packages_dir()
+        pthfile_lines = self.requirements().pths_as_absolute(self.topsrcdir)
         with open(os.path.join(site_packages_dir, PTH_FILENAME), "a") as f:
-            for pth_requirement in (
-                env_requirements.pth_requirements
-                + env_requirements.vendored_requirements
-            ):
-                path = os.path.join(self.topsrcdir, pth_requirement.path)
-                # This path is relative to the .pth file.  Using a
-                # relative path allows the srcdir/objdir combination
-                # to be moved around (as long as the paths relative to
-                # each other remain the same).
-                f.write("{}\n".format(os.path.relpath(path, site_packages_dir)))
+            f.write("\n".join(pthfile_lines))
 
         old_env_variables = {}
         try:
diff --git a/python/mach_commands.py b/python/mach_commands.py
index f3293a2cc44a..4f07506468e8 100644
--- a/python/mach_commands.py
+++ b/python/mach_commands.py
@@ -80,9 +80,7 @@ def python(
         )
 
         append_env["PYTHONPATH"] = os.pathsep.join(
-            os.path.join(command_context.topsrcdir, pth.path)
-            for pth in requirements.pth_requirements
-            + requirements.vendored_requirements
+            requirements.pths_as_absolute(command_context.topsrcdir)
         )
     else:
         command_context.virtualenv_manager.ensure()