diff --git a/py-polars/polars/dataframe/groupby.py b/py-polars/polars/dataframe/groupby.py
index ac92466d3038..6f5dea8838b0 100644
--- a/py-polars/polars/dataframe/groupby.py
+++ b/py-polars/polars/dataframe/groupby.py
@@ -452,6 +452,9 @@ def count(self) -> DF:
         """
         Count the number of values in each group.
 
+        .. warning::
+            `null` is deemed a value in this context.
+
         Examples
         --------
         >>> df = pl.DataFrame(
diff --git a/py-polars/polars/expr/expr.py b/py-polars/polars/expr/expr.py
index 9e6cc68f956e..fbb3f8382d54 100644
--- a/py-polars/polars/expr/expr.py
+++ b/py-polars/polars/expr/expr.py
@@ -1124,6 +1124,9 @@ def count(self) -> Self:
         """
         Count the number of values in this expression.
 
+        .. warning::
+            `null` is deemed a value in this context.
+
         Examples
         --------
         >>> df = pl.DataFrame({"a": [8, 9, 10], "b": [None, 4, 4]})
diff --git a/py-polars/polars/functions/lazy.py b/py-polars/polars/functions/lazy.py
index 1058a6e4ccff..e6688e9594ed 100644
--- a/py-polars/polars/functions/lazy.py
+++ b/py-polars/polars/functions/lazy.py
@@ -291,6 +291,9 @@ def count(column: str | Series | None = None) -> Expr | int:
     """
     Count the number of values in this column/context.
 
+    .. warning::
+        `null` is deemed a value in this context.
+
     Parameters
     ----------
     column
diff --git a/py-polars/polars/lazyframe/groupby.py b/py-polars/polars/lazyframe/groupby.py
index 03fd999c01ad..a824bb30a846 100644
--- a/py-polars/polars/lazyframe/groupby.py
+++ b/py-polars/polars/lazyframe/groupby.py
@@ -346,6 +346,9 @@ def count(self) -> LDF:
         """
         Count the number of values in each group.
 
+        .. warning::
+            `null` is deemed a value in this context.
+
         Examples
         --------
         >>> ldf = pl.DataFrame(