diff --git a/crates/polars-core/src/utils/supertype.rs b/crates/polars-core/src/utils/supertype.rs
index 47ecd9c13a4f..1f1d7f9751c8 100644
--- a/crates/polars-core/src/utils/supertype.rs
+++ b/crates/polars-core/src/utils/supertype.rs
@@ -304,6 +304,7 @@ pub fn get_supertype(l: &DataType, r: &DataType) -> Option<DataType> {
                             }
                         }
                     }
+                    UnknownKind::Int(_) if dt.is_decimal() => Some(dt.clone()),
                     _ => Some(Unknown(UnknownKind::Any))
                 }
             },
diff --git a/py-polars/tests/unit/datatypes/test_decimal.py b/py-polars/tests/unit/datatypes/test_decimal.py
index 1e95adb4a3e7..9d14e0b8c549 100644
--- a/py-polars/tests/unit/datatypes/test_decimal.py
+++ b/py-polars/tests/unit/datatypes/test_decimal.py
@@ -461,3 +461,13 @@ def test_decimal_streaming() -> None:
             D("161102921617598.363263936811563000"),
         ],
     }
+
+
+def test_decimal_supertype() -> None:
+    with pl.Config() as cfg:
+        cfg.activate_decimals()
+        pl.Config.activate_decimals()
+        q = pl.LazyFrame([0.12345678]).select(
+            pl.col("column_0").cast(pl.Decimal(scale=6)) * 1
+        )
+        assert q.collect().dtypes[0].is_decimal()