diff --git a/readthedocs/doc_builder/environments.py b/readthedocs/doc_builder/environments.py
index 23c23ee0e1e..30d8ad4bc95 100644
--- a/readthedocs/doc_builder/environments.py
+++ b/readthedocs/doc_builder/environments.py
@@ -103,11 +103,9 @@ def __init__(
         if cwd is None:
             cwd = os.getcwd()
         self.cwd = cwd
-        self.environment = os.environ.copy()
-        if environment is not None:
-            if 'PATH' in environment:
-                raise BuildEnvironmentError('\'PATH\' can\'t be set.')
-            self.environment.update(environment)
+
+        environment = environment or {}
+        self.environment = environment.copy()
 
         self.combine_output = combine_output
         self.input_data = input_data
@@ -150,13 +148,7 @@ def run(self):
         if self.combine_output:
             stderr = subprocess.STDOUT
 
-        environment = {}
-        environment.update(self.environment)
-        environment['READTHEDOCS'] = 'True'
-        if self.build_env is not None:
-            environment['READTHEDOCS_VERSION'] = self.build_env.version.slug
-            environment['READTHEDOCS_PROJECT'] = self.build_env.project.slug
-            environment['READTHEDOCS_LANGUAGE'] = self.build_env.project.language
+        environment = self.environment.copy()
         if 'DJANGO_SETTINGS_MODULE' in environment:
             del environment['DJANGO_SETTINGS_MODULE']
         if 'PYTHONPATH' in environment:
@@ -329,6 +321,7 @@ def run(self):
             exec_cmd = client.exec_create(
                 container=self.build_env.container_id,
                 cmd=self.get_wrapped_command(),
+                environment=self.environment,
                 stdout=True,
                 stderr=True,
             )
@@ -1051,7 +1044,6 @@ def create_container(self):
                 volumes=self._get_binds(),
                 host_config=self.get_container_host_config(),
                 detach=True,
-                environment=self.environment,
                 user=settings.RTD_DOCKER_USER,
             )
             client.start(container=self.container_id)
diff --git a/readthedocs/projects/tasks.py b/readthedocs/projects/tasks.py
index 2874c680908..8b8fbd7333d 100644
--- a/readthedocs/projects/tasks.py
+++ b/readthedocs/projects/tasks.py
@@ -725,7 +725,7 @@ def setup_vcs(self, environment):
     def get_env_vars(self):
         """Get bash environment variables used for all builder commands."""
         env = {
-            'READTHEDOCS': True,
+            'READTHEDOCS': 'True',
             'READTHEDOCS_VERSION': self.version.slug,
             'READTHEDOCS_PROJECT': self.project.slug,
             'READTHEDOCS_LANGUAGE': self.project.language,
diff --git a/readthedocs/vcs_support/base.py b/readthedocs/vcs_support/base.py
index b482f0796d5..43fc8b84857 100644
--- a/readthedocs/vcs_support/base.py
+++ b/readthedocs/vcs_support/base.py
@@ -81,12 +81,7 @@ def make_clean_working_dir(self):
 
     @property
     def env(self):
-        environment = os.environ.copy()
-
-        # TODO: kind of a hack
-        del environment['PATH']
-
-        return environment
+        return {}
 
     def update(self):
         """