diff --git a/polars/polars-time/src/groupby/dynamic.rs b/polars/polars-time/src/groupby/dynamic.rs
index b464b75d00509..ad4eb11a2230e 100644
--- a/polars/polars-time/src/groupby/dynamic.rs
+++ b/polars/polars-time/src/groupby/dynamic.rs
@@ -252,6 +252,7 @@ impl Wrap<&DataFrame> {
         let groups = if by.is_empty() {
             let vals = dt.downcast_iter().next().unwrap();
             let ts = vals.values().as_slice();
+            partially_check_sorted(ts);
             let (groups, lower, upper) = groupby_windows(
                 w,
                 ts,
diff --git a/polars/polars-time/src/windows/groupby.rs b/polars/polars-time/src/windows/groupby.rs
index c2fef164cb9cd..387996a47e20d 100644
--- a/polars/polars-time/src/windows/groupby.rs
+++ b/polars/polars-time/src/windows/groupby.rs
@@ -360,13 +360,13 @@ pub(crate) fn groupby_values_iter_full_lookahead(
         })
 }
 
-fn partially_check_sorted(time: &[i64]) {
+pub(crate) fn partially_check_sorted(time: &[i64]) {
     // check sortedness of a small subslice.
     if time.len() > 1 {
         assert!(time[..std::cmp::min(time.len(), 10)].windows(2).filter_map(|w| match w[0].cmp(&w[1]) {
             Ordering::Equal => None,
             t => Some(t)
-        }).all_equal(), "Subslice check showed that the values in `groupby_rolling` were not sorted. Pleasure ensure the index column is sorted.");
+        }).all_equal(), "Subslice check showed that the values in `groupby_rolling/groupby_dynamic` were not sorted. Pleasure ensure the index column is sorted.");
     }
 }
 
diff --git a/py-polars/polars/internals/dataframe/frame.py b/py-polars/polars/internals/dataframe/frame.py
index ac3ae8c5fc44c..da4e31348abd1 100644
--- a/py-polars/polars/internals/dataframe/frame.py
+++ b/py-polars/polars/internals/dataframe/frame.py
@@ -3677,6 +3677,9 @@ def groupby_dynamic(
         - "1i"      # length 1
         - "10i"     # length 10
 
+        .. warning::
+            The index column must be sorted in ascending order.
+
         Parameters
         ----------
         index_column
diff --git a/py-polars/polars/internals/lazyframe/frame.py b/py-polars/polars/internals/lazyframe/frame.py
index d0e5de25db273..b113114108008 100644
--- a/py-polars/polars/internals/lazyframe/frame.py
+++ b/py-polars/polars/internals/lazyframe/frame.py
@@ -1884,6 +1884,9 @@ def groupby_dynamic(
         - "1i"      # length 1
         - "10i"     # length 10
 
+        .. warning::
+            The index column must be sorted in ascending order.
+
         Parameters
         ----------
         index_column