diff --git a/tests/run-tests.py b/tests/run-tests.py
index 801367447ce33d426f1c99618806ac8eaf37319e_dGVzdHMvcnVuLXRlc3RzLnB5..ba8aa20ff31fe3fede1447f39324d0397a2754d5_dGVzdHMvcnVuLXRlc3RzLnB5 100755
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -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: