diff --git a/crates/polars-ops/src/frame/join/dispatch_left_right.rs b/crates/polars-ops/src/frame/join/dispatch_left_right.rs
index 452c51154a64..4267c8743bc6 100644
--- a/crates/polars-ops/src/frame/join/dispatch_left_right.rs
+++ b/crates/polars-ops/src/frame/join/dispatch_left_right.rs
@@ -170,8 +170,7 @@ fn maintain_order_idx(
     let join_tuples_left = df
         .column("a")
         .unwrap()
-        .as_series()
-        .unwrap()
+        .as_materialized_series()
         .idx()
         .unwrap()
         .cont_slice()
@@ -180,8 +179,7 @@ fn maintain_order_idx(
     let join_tuples_right = df
         .column("b")
         .unwrap()
-        .as_series()
-        .unwrap()
+        .as_materialized_series()
         .idx()
         .unwrap()
         .cont_slice()
diff --git a/py-polars/tests/unit/functions/test_functions.py b/py-polars/tests/unit/functions/test_functions.py
index 05bd11976fd8..37fb0e8eae73 100644
--- a/py-polars/tests/unit/functions/test_functions.py
+++ b/py-polars/tests/unit/functions/test_functions.py
@@ -374,6 +374,14 @@ def test_align_frames_duplicate_key() -> None:
     ]
 
 
+def test_align_frames_single_row_20445() -> None:
+    left = pl.DataFrame({"a": [1], "b": [2]})
+    right = pl.DataFrame({"a": [1], "c": [3]})
+    result = pl.align_frames(left, right, how="left", on="a")
+    assert_frame_equal(result[0], left)
+    assert_frame_equal(result[1], right)
+
+
 def test_coalesce() -> None:
     df = pl.DataFrame(
         {