Index: utils/lit/tests/Inputs/shtest-timeout/lit.cfg
===================================================================
--- utils/lit/tests/Inputs/shtest-timeout/lit.cfg
+++ utils/lit/tests/Inputs/shtest-timeout/lit.cfg
@@ -28,5 +28,12 @@
 config.test_exec_root = config.test_source_root
 config.target_triple = '(unused)'
 src_root = os.path.join(config.test_source_root, '..')
-config.environment['PYTHONPATH'] = src_root
+
+pythonpath_list = [src_root]
+if 'PYTHONPATH' in os.environ:
+    pythonpath_list.append(os.environ['PYTHONPATH'])
+if 'PYTHONPATH' in config.environment:
+    pythonpath_list.append(config.environment['PYTHONPATH'])
+config.environment['PYTHONPATH'] = os.pathsep.join(pythonpath_list)
+
 config.substitutions.append(('%{python}', sys.executable))
Index: utils/lit/tests/lit.cfg
===================================================================
--- utils/lit/tests/lit.cfg
+++ utils/lit/tests/lit.cfg
@@ -34,7 +34,15 @@
 else:
   lit_path = src_root
 
-config.environment['PYTHONPATH'] = lit_path # Required because some tests import the lit module
+pythonpath_list = [lit_path] # Required because some tests import the lit module
+
+# Ensure the user's PYTHONPATH is included.
+if 'PYTHONPATH' in os.environ:
+    pythonpath_list.append(os.environ['PYTHONPATH'])
+if 'PYTHONPATH' in config.environment:
+    pythonpath_list.append(config.environment['PYTHONPATH'])
+config.environment['PYTHONPATH'] = os.pathsep.join(pythonpath_list)
+
 config.substitutions.append(('%{src_root}', src_root))
 config.substitutions.append(('%{inputs}', os.path.join(
             src_root, 'tests', 'Inputs')))