diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2dd42bc..0a40d4b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,6 +24,13 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
         python-version: ["3.9", "3.11", "3.12"]
     runs-on: ${{ matrix.os }}
+    env:
+      # Force UTF-8 mode on all platforms. Without this, Windows defaults to
+      # cp1252 ('charmap'), which fails when importing upstream packages that
+      # read their own source / data files without an explicit encoding
+      # (seen with trl.trainer.grpo_trainer on windows-latest / py3.11).
+      PYTHONUTF8: "1"
+      PYTHONIOENCODING: "utf-8"
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
diff --git a/tests/test_bugfixes.py b/tests/test_bugfixes.py
index eea5c82..8ade37c 100644
--- a/tests/test_bugfixes.py
+++ b/tests/test_bugfixes.py
@@ -662,11 +662,34 @@ class TestPPOExperimentalSetup:
 # --- BUG-008: GRPO CPU empty generation tensor mismatch (v0.10.6) ---
 
 
+def _trl_grpo_importable() -> bool:
+    """Detect whether trl.trainer.grpo_trainer can be imported on this host.
+
+    Upstream trl occasionally ships source files that read auxiliary data
+    without an explicit encoding. On Windows with the default cp1252
+    (``charmap``) codec this fails at import time with a ``UnicodeDecodeError``.
+    Our CI forces ``PYTHONUTF8=1`` for safety; this helper is a belt-and-braces
+    check so the test skips cleanly instead of erroring out if the env var is
+    missing locally.
+    """
+    try:
+        import trl  # noqa: F401
+        import trl.trainer.grpo_trainer  # noqa: F401
+    except (UnicodeDecodeError, ImportError, RuntimeError):
+        return False
+    return True
+
+
 class TestGRPOCPUMinNewTokens:
     """Test GRPO CPU workaround: generation_kwargs with min_new_tokens."""
 
     def test_cpu_adds_generation_kwargs(self):
         """On CPU, GRPO setup should add generation_kwargs with min_new_tokens."""
+        if not _trl_grpo_importable():
+            pytest.skip(
+                "trl.trainer.grpo_trainer not importable on this host "
+                "(likely Windows cp1252 without PYTHONUTF8=1)"
+            )
         from unittest.mock import MagicMock
         from unittest.mock import patch as mock_patch
 
@@ -711,6 +734,11 @@ class TestGRPOCPUMinNewTokens:
 
     def test_gpu_no_generation_kwargs(self):
         """On GPU, GRPO setup should NOT add generation_kwargs for min_new_tokens."""
+        if not _trl_grpo_importable():
+            pytest.skip(
+                "trl.trainer.grpo_trainer not importable on this host "
+                "(likely Windows cp1252 without PYTHONUTF8=1)"
+            )
         from unittest.mock import MagicMock
         from unittest.mock import patch as mock_patch