diff --git a/supervisor/options.py b/supervisor/options.py
index 3dc84afd9..fae938e02 100644
--- a/supervisor/options.py
+++ b/supervisor/options.py
@@ -1955,7 +1955,8 @@ def make_dispatchers(self, proc):
     def load_external_environment_definition(self):
         return self.load_external_environment_definition_for_config(self)
 
-    # this is separated out in order to make it easier to test
+    # NOTE - THIS IS BLOCKING CODE AND MUST ONLY BE CALLED IN TESTS OR IN CHILD PROCESSES, NOT THE
+    # MAIN SUPERVISORD THREAD OF EXECUTION
     @classmethod
     def load_external_environment_definition_for_config(cls, config):
         # lazily load extra env vars before we drop privileges so that this can be used to load a secrets file
@@ -1976,21 +1977,15 @@ def load_external_environment_definition_for_config(cls, config):
 
         elif config.environment_loader:
             try:
-                from subprocess import check_output, CalledProcessError
-                kwargs = dict(shell=True)
-                if sys.version_info.major >= 3:
-                    if sys.version_info.minor >= 7:
-                        kwargs['text'] = True
-                    else:
-                        pass  # we will decode the bytes returned after reading it for these versions of python
-
-                envdata = check_output(config.environment_loader, **kwargs)
+                from subprocess import check_output, CalledProcessError, STDOUT as subprocess_STDOUT
 
-                if sys.version_info.major >= 3 and sys.version_info.minor < 7:
-                    envdata = envdata.decode('utf8')
+                envdata = check_output(config.environment_loader, shell=True, stderr=subprocess_STDOUT)
+                envdata = as_string(envdata)
 
             except CalledProcessError as e:
-                raise ProcessException("environment_loader failure with %s: %d, %s" % (config.environment_loader, e.returncode, e.output))
+                raise ProcessException("environment_loader failure with %s: %d, %s" % \
+                    (config.environment_loader, e.returncode, as_string(e.stdout))
+                )
 
         if envdata:
             extra_env = {}
diff --git a/supervisor/process.py b/supervisor/process.py
index b047886e5..e303a6b2d 100644
--- a/supervisor/process.py
+++ b/supervisor/process.py
@@ -218,9 +218,6 @@ def spawn(self):
         try:
             filename, argv = self.get_execv_args()
 
-            # check the environment_file/environment_loader options before we fork to simplify child process management
-            extra_env = self.config.load_external_environment_definition()
-
         except ProcessException as what:
             self.record_spawnerr(what.args[0])
             self._assertInState(ProcessStates.STARTING)
@@ -264,7 +261,7 @@ def spawn(self):
             return self._spawn_as_parent(pid)
 
         else:
-            return self._spawn_as_child(filename, argv, extra_env=extra_env)
+            return self._spawn_as_child(filename, argv)
 
     def _spawn_as_parent(self, pid):
         # Parent
@@ -288,9 +285,17 @@ def _prepare_child_fds(self):
         for i in range(3, options.minfds):
             options.close_fd(i)
 
-    def _spawn_as_child(self, filename, argv, extra_env=None):
+    def _spawn_as_child(self, filename, argv):
         options = self.config.options
         try:
+            # check the environment_file/environment_loader options after forking in order to avoid blocking the
+            # main supervisord thread, but do it before we start to mix up the process signals/state
+            try:
+                extra_env = self.config.load_external_environment_definition()
+            except ProcessException as e:
+                self.record_spawnerr(e.args[0])
+                raise
+
             # prevent child from receiving signals sent to the
             # parent by calling os.setpgrp to create a new process
             # group for the child; this prevents, for instance,