--- a/tests/run-tests.py	Wed Jan 29 18:55:30 2025 +0100
+++ b/tests/run-tests.py	Wed Jan 29 18:56:20 2025 +0100
@@ -3425,6 +3425,7 @@
         if self.options.pure:
             os.environ["HGTEST_RUN_TESTS_PURE"] = "--pure"
             os.environ["HGMODULEPOLICY"] = "py"
+            os.environ.pop("HGWITHRUSTEXT", None)
         if self.options.rust:
             os.environ["HGMODULEPOLICY"] = "rust+c"
         if self.options.no_rust: