diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 94db66b6db..e604640fc8 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -53,6 +53,10 @@ Fixed
 
 * StackStorm now explicitly decodes pack files as utf-8 instead of implicitly as ascii (bug fix) #5106, #5107
 
+* Kept functionality for implicit relative imports in Python actions (regression, bug fix) #5127
+
+  Identified by @amanda11
+
 Removed
 ~~~~~~~~
 * Removed --python3 pack install option  #5100
diff --git a/st2common/st2common/util/sandboxing.py b/st2common/st2common/util/sandboxing.py
index 6b3c4e29b9..b6b629a72e 100644
--- a/st2common/st2common/util/sandboxing.py
+++ b/st2common/st2common/util/sandboxing.py
@@ -20,6 +20,7 @@
 
 from __future__ import absolute_import
 
+import fnmatch
 import os
 import sys
 from distutils.sysconfig import get_python_lib
@@ -27,6 +28,7 @@
 from oslo_config import cfg
 
 from st2common.constants.pack import SYSTEM_PACK_NAMES
+from st2common.content.utils import get_pack_base_path
 
 __all__ = [
     'get_sandbox_python_binary_path',
@@ -132,10 +134,67 @@ def get_sandbox_python_path_for_python_action(pack, inherit_from_parent=True,
     Same as get_sandbox_python_path() function, but it's intended to be used for Python runner
     actions.
     """
-    return get_sandbox_python_path(
+    sandbox_python_path = get_sandbox_python_path(
         inherit_from_parent=inherit_from_parent,
         inherit_parent_virtualenv=inherit_parent_virtualenv)
 
+    virtualenv_path = get_sandbox_virtualenv_path(pack=pack)
+
+    if virtualenv_path and os.path.isdir(virtualenv_path):
+        # Get the pack's virtualenv site-packages directory
+        # There should only be one, but we don't know what version of Python it
+        # will be using, so we use a glob and ensure it exists
+        virtualenv_lib_path = os.path.join(virtualenv_path, 'lib')
+        virtualenv_lib_directories = [
+            dir_name for dir_name in os.listdir(virtualenv_lib_path)
+            if fnmatch.fnmatch(dir_name, 'python*')
+        ]
+
+        if virtualenv_lib_directories:
+            pack_base_path = get_pack_base_path(pack_name=pack)
+            # This will be just the virtualenv's Python version - eg: python3.6
+            virtualenv_lib_directory = virtualenv_lib_directories[0]
+
+            # Get the pack's actions/lib directory
+            pack_actions_lib_paths = os.path.join(pack_base_path, 'actions', 'lib')
+            # Get the pack's virtualenv's site-packages directory
+            virtualenv_lib_directory = os.path.join(virtualenv_lib_path, virtualenv_lib_directory)
+
+            # Work around to make sure we also add system lib dir to PYTHONPATH
+            # and not just virtualenv one (e.g. /usr/lib/python3.6)
+            # This code will pick the same sytem Python version as exists in
+            # the virtualenv, since virtualenv_lib_directory identifies that
+            # directory within the virtualenv and it should have the same name
+            # as the system Python executable.
+
+            # NOTE: We can't simply use sys.prefix dir since it will be set to /opt/stackstorm/st2
+
+            # By default, Python libs are installed either in /usr/lib/python3.x or
+            # /usr/local/lib/python3.x
+            for system_prefix_dir in ['/usr/lib', '/usr/local/lib']:
+                system_lib_directory = os.path.join(system_prefix_dir,
+                                                    virtualenv_lib_directory)
+
+                if os.path.exists(system_lib_directory):
+                    break
+            else:
+                # If no system library is found
+                system_lib_directory = None
+
+            full_sandbox_python_path = []
+
+            # NOTE: Order here is very important for imports to function correctly
+            if system_lib_directory:
+                full_sandbox_python_path.append(system_lib_directory)
+
+            full_sandbox_python_path.append(virtualenv_lib_directory)
+            full_sandbox_python_path.append(pack_actions_lib_paths)
+            full_sandbox_python_path.append(sandbox_python_path)
+
+            sandbox_python_path = ':'.join(full_sandbox_python_path)
+
+    return sandbox_python_path
+
 
 def get_sandbox_virtualenv_path(pack):
     """
diff --git a/st2common/tests/unit/test_util_sandboxing.py b/st2common/tests/unit/test_util_sandboxing.py
index af3c4328da..e1da46e257 100644
--- a/st2common/tests/unit/test_util_sandboxing.py
+++ b/st2common/tests/unit/test_util_sandboxing.py
@@ -111,6 +111,8 @@ def test_get_sandbox_python_path(self, mock_get_python_lib):
 
     @mock.patch('os.path.isdir', mock.Mock(return_value=True))
     @mock.patch('os.listdir', mock.Mock(return_value=['python2.7']))
+    @mock.patch('st2common.util.sandboxing.get_sandbox_virtualenv_path',
+                mock.Mock(return_value=None))
     @mock.patch('st2common.util.sandboxing.get_python_lib')
     def test_get_sandbox_python_path_for_python_action_python2_used_for_venv(self,
             mock_get_python_lib):