diff --git a/.github/workflows/package.yml b/.github/workflows/package.yml
index 26a6a7e..bb2fa60 100644
--- a/.github/workflows/package.yml
+++ b/.github/workflows/package.yml
@@ -35,6 +35,7 @@ jobs:
       - name: Run packaging step
         env:
           UV_PYTHON: "3.12"
+          UV_PYTHON_PREFERENCE: only-managed
           ISIC_CLI_SENTRY_DSN: ${{ secrets.ISIC_CLI_SENTRY_DSN }}
         run: |
           uv run tox -e package
@@ -71,6 +72,11 @@ jobs:
           uv run tox -e package
         env:
           ISIC_CLI_SENTRY_DSN: ${{ secrets.ISIC_CLI_SENTRY_DSN }}
+          # the runners ship a python.org build of Python on PATH, which uv picks over downloading
+          # a managed one. python.org builds split the stdlib into ~50 separate extension modules,
+          # and on macOS every freshly extracted shared library costs ~120ms per launch of the
+          # onefile binary. python-build-standalone compiles them into libpython.
+          UV_PYTHON_PREFERENCE: only-managed
       - name: Zip and upload binary
         run: |
           .github/zip_and_upload_package.sh ${{ runner.os }} ${{ github.event.release.tag_name }}
diff --git a/tox.ini b/tox.ini
index 32c910f..4ac6edc 100644
--- a/tox.ini
+++ b/tox.ini
@@ -45,6 +45,12 @@ passenv =
     ISIC_CLI_SENTRY_DSN
 dependency_groups =
     package
+# charset_normalizer ships mypyc-compiled extensions with pure python fallbacks. on macOS, each
+# shared library extracted by the onefile binary costs ~120ms per launch, so build it from source
+# to get the pure python version instead.
+uv_sync_flags =
+    --no-binary-package
+    charset-normalizer
 commands =
     python scripts/write_sentry_dsn_module.py {env_tmp_dir}/sentry_dsn/_isic_cli_sentry_dsn.py
     pyinstaller \