diff --git a/Misc/NEWS b/Misc/NEWS
index 0bb54c5f889..50ac145daad 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -149,6 +149,12 @@ Build
 - Issue #20609: Restored the ability to build 64-bit Windows binaries on
   32-bit Windows, which was broken by the change in issue #19788.
 
+Tools/Demos
+-----------
+
+- Issue #20535: PYTHONWARNING no longer affects the run_tests.py script.
+  Patch by Arfrever Frehtes Taifersar Arahesis.
+
 
 What's New in Python 3.3.4?
 ===========================
diff --git a/Tools/scripts/run_tests.py b/Tools/scripts/run_tests.py
index e2a20509781..a6c5da35e2f 100644
--- a/Tools/scripts/run_tests.py
+++ b/Tools/scripts/run_tests.py
@@ -32,6 +32,12 @@ def main(regrtest_args):
             ]
     # Allow user-specified interpreter options to override our defaults.
     args.extend(test.support.args_from_interpreter_flags())
+
+    # Workaround for issue #20355
+    os.environ.pop("PYTHONWARNINGS", None)
+    # Workaround for issue #20361
+    args.extend(['-W', 'error::BytesWarning'])
+
     args.extend(['-m', 'test',    # Run the test suite
                  '-r',            # Randomize test order
                  '-w',            # Re-run failed tests in verbose mode