diff --git a/narwhals/_pandas_like/dataframe.py b/narwhals/_pandas_like/dataframe.py
index 2fba95dfe..47c43a69a 100644
--- a/narwhals/_pandas_like/dataframe.py
+++ b/narwhals/_pandas_like/dataframe.py
@@ -767,19 +767,24 @@ def to_numpy(self, dtype: Any = None, copy: bool | None = None) -> Any:
     def to_pandas(self: Self) -> pd.DataFrame:
         if self._implementation is Implementation.PANDAS:
             return self._native_frame
-        if self._implementation is Implementation.MODIN:
+        elif self._implementation is Implementation.CUDF:  # pragma: no cover
+            return self._native_frame.to_pandas()
+        elif self._implementation is Implementation.MODIN:
             return self._native_frame._to_pandas()
-        return self._native_frame.to_pandas()  # pragma: no cover
+        msg = f"Unknown implementation: {self._implementation}"  # pragma: no cover
+        raise AssertionError(msg)
 
     def to_polars(self: Self) -> pl.DataFrame:
         import polars as pl  # ignore-banned-import
 
         if self._implementation is Implementation.PANDAS:
             return pl.from_pandas(self._native_frame)
-        if self._implementation is Implementation.MODIN:
-            return self._native_frame._to_polars()  # type: ignore[no-any-return]
-
-        raise NotImplementedError
+        elif self._implementation is Implementation.CUDF:  # pragma: no cover
+            return pl.from_pandas(self._native_frame.to_pandas())
+        elif self._implementation is Implementation.MODIN:
+            return pl.from_pandas(self._native_frame._to_pandas())
+        msg = f"Unknown implementation: {self._implementation}"  # pragma: no cover
+        raise AssertionError(msg)
 
     def write_parquet(self, file: Any) -> Any:
         self._native_frame.to_parquet(file)
diff --git a/narwhals/_pandas_like/series.py b/narwhals/_pandas_like/series.py
index db7cb0871..358041db7 100644
--- a/narwhals/_pandas_like/series.py
+++ b/narwhals/_pandas_like/series.py
@@ -842,7 +842,7 @@ def to_numpy(self, dtype: Any = None, copy: bool | None = None) -> Any:
     def to_pandas(self: Self) -> pd.Series:
         if self._implementation is Implementation.PANDAS:
             return self._native_series
-        elif self._implementation is Implementation.CUDF:
+        elif self._implementation is Implementation.CUDF:  # pragma: no cover
             return self._native_series.to_pandas()
         elif self._implementation is Implementation.MODIN:
             return self._native_series._to_pandas()
@@ -854,10 +854,12 @@ def to_polars(self: Self) -> pl.DataFrame:
 
         if self._implementation is Implementation.PANDAS:
             return pl.from_pandas(self._native_series)
-        if self._implementation is Implementation.MODIN:
-            return self._native_series._to_polars()  # type: ignore[no-any-return]
-
-        raise NotImplementedError
+        elif self._implementation is Implementation.CUDF:  # pragma: no cover
+            return pl.from_pandas(self._native_series.to_pandas())
+        elif self._implementation is Implementation.MODIN:
+            return pl.from_pandas(self._native_series._to_pandas())
+        msg = f"Unknown implementation: {self._implementation}"  # pragma: no cover
+        raise AssertionError(msg)
 
     # --- descriptive ---
     def is_duplicated(self: Self) -> Self: