diff --git a/crates/polars-sql/src/functions.rs b/crates/polars-sql/src/functions.rs
index 58fb6bf8ca92a..9c19169500676 100644
--- a/crates/polars-sql/src/functions.rs
+++ b/crates/polars-sql/src/functions.rs
@@ -768,15 +768,15 @@ impl SQLFunctionVisitor<'_> {
                 1 => self.visit_unary(|e| e.round(0)),
                 2 => self.try_visit_binary(|e, decimals| {
                     Ok(e.round(match decimals {
-                        Expr::Literal(LiteralValue::Int64(n)) => n as u32,
-                        _ => {
-                            polars_bail!(InvalidOperation: "Invalid 'decimals' for Round: {}", function.args[1]);
-                        }
+                        Expr::Literal(LiteralValue::Int64(n)) => {
+                            if n >= 0 { n as u32 } else {
+                                polars_bail!(InvalidOperation: "Round does not (yet) support negative 'decimals': {}", function.args[1]);
+                            }
+                        },
+                        _ => polars_bail!(InvalidOperation: "Invalid 'decimals' for Round: {}", function.args[1]);
                     }))
                 }),
-                _ => {
-                    polars_bail!(InvalidOperation:"Invalid number of arguments for Round: {}", function.args.len());
-                },
+                _ => polars_bail!(InvalidOperation:"Invalid number of arguments for Round: {}", function.args.len());
             },
             Sign => self.visit_unary(Expr::sign),
             Sqrt => self.visit_unary(Expr::sqrt),
diff --git a/py-polars/tests/unit/sql/test_numeric.py b/py-polars/tests/unit/sql/test_numeric.py
index 7d7938465ca57..09cbcc237739f 100644
--- a/py-polars/tests/unit/sql/test_numeric.py
+++ b/py-polars/tests/unit/sql/test_numeric.py
@@ -107,10 +107,15 @@ def test_round_ndigits(decimals: int, expected: list[float]) -> None:
 
 def test_round_ndigits_errors() -> None:
     df = pl.DataFrame({"n": [99.999]})
-    with pl.SQLContext(df=df, eager_execution=True) as ctx, pytest.raises(
-        InvalidOperationError, match="Invalid 'decimals' for Round: -1"
-    ):
-        ctx.execute("SELECT ROUND(n,-1) AS n FROM df")
+    with pl.SQLContext(df=df, eager_execution=True) as ctx:
+        with pytest.raises(
+            InvalidOperationError, match="Invalid 'decimals' for Round: ??"
+        ):
+            ctx.execute("SELECT ROUND(n,'??') AS n FROM df")
+        with pytest.raises(
+            InvalidOperationError, match="Round .* negative 'decimals': -1"
+        ):
+            ctx.execute("SELECT ROUND(n,-1) AS n FROM df")
 
 
 def test_stddev_variance() -> None: