diff --git a/crates/polars-lazy/src/physical_plan/planner/lp.rs b/crates/polars-lazy/src/physical_plan/planner/lp.rs
index 68cfbc09ad2a..f2ccf79706d0 100644
--- a/crates/polars-lazy/src/physical_plan/planner/lp.rs
+++ b/crates/polars-lazy/src/physical_plan/planner/lp.rs
@@ -431,11 +431,11 @@ pub fn create_physical_plan(
                 let input = create_physical_plan(input, lp_arena, expr_arena)?;
                 let keys = keys
                     .iter()
-                    .map(|e| node_to_expr(e.node(), expr_arena))
+                    .map(|e| e.to_expr(expr_arena))
                     .collect::<Vec<_>>();
                 let aggs = aggs
                     .iter()
-                    .map(|e| node_to_expr(e.node(), expr_arena))
+                    .map(|e| e.to_expr(expr_arena))
                     .collect::<Vec<_>>();
                 Ok(Box::new(executors::PartitionGroupByExec::new(
                     input,
diff --git a/crates/polars-lazy/src/physical_plan/streaming/convert_alp.rs b/crates/polars-lazy/src/physical_plan/streaming/convert_alp.rs
index 8b2727dc3d45..acd293dead12 100644
--- a/crates/polars-lazy/src/physical_plan/streaming/convert_alp.rs
+++ b/crates/polars-lazy/src/physical_plan/streaming/convert_alp.rs
@@ -386,7 +386,7 @@ pub(crate) fn insert_streaming_nodes(
                 aggs,
                 maintain_order: false,
                 apply: None,
-                schema,
+                schema: output_schema,
                 options,
                 ..
             } => {
@@ -435,17 +435,15 @@ pub(crate) fn insert_streaming_nodes(
 
                 let valid_key = || {
                     keys.iter().all(|e| {
-                        expr_arena
-                            .get(e.node())
-                            .get_type(schema, Context::Default, expr_arena)
-                            // ensure we don't group_by list
+                        output_schema
+                            .get(e.output_name())
                             .map(|dt| !matches!(dt, DataType::List(_)))
                             .unwrap_or(false)
                     })
                 };
 
                 let valid_types = || {
-                    schema
+                    output_schema
                         .iter_dtypes()
                         .all(|dt| allowed_dtype(dt, string_cache))
                 };
diff --git a/crates/polars-plan/src/logical_plan/expr_ir.rs b/crates/polars-plan/src/logical_plan/expr_ir.rs
index 7a1b47d2cb57..f5f0b0ddf12a 100644
--- a/crates/polars-plan/src/logical_plan/expr_ir.rs
+++ b/crates/polars-plan/src/logical_plan/expr_ir.rs
@@ -94,11 +94,11 @@ impl ExprIR {
         self.output_name.unwrap()
     }
 
-    pub(crate) fn output_name(&self) -> &str {
+    pub fn output_name(&self) -> &str {
         self.output_name_arc().as_ref()
     }
 
-    pub(crate) fn to_expr(&self, expr_arena: &Arena<AExpr>) -> Expr {
+    pub fn to_expr(&self, expr_arena: &Arena<AExpr>) -> Expr {
         let out = node_to_expr(self.node, expr_arena);
 
         match &self.output_name {
diff --git a/py-polars/polars/testing/__init__.py b/py-polars/polars/testing/__init__.py
index b5962f7fba2c..06b4f6c91419 100644
--- a/py-polars/polars/testing/__init__.py
+++ b/py-polars/polars/testing/__init__.py
@@ -10,4 +10,5 @@
     "assert_frame_not_equal",
     "assert_series_equal",
     "assert_series_not_equal",
+    "_constants",
 ]
diff --git a/py-polars/polars/testing/_constants.py b/py-polars/polars/testing/_constants.py
new file mode 100644
index 000000000000..8c11b6d0f176
--- /dev/null
+++ b/py-polars/polars/testing/_constants.py
@@ -0,0 +1,2 @@
+# On this limit Polars will start partitioning in debug builds
+PARTITION_LIMIT = 15
diff --git a/py-polars/tests/unit/streaming/test_streaming_group_by.py b/py-polars/tests/unit/streaming/test_streaming_group_by.py
index 506422dc38dd..e7915115b79a 100644
--- a/py-polars/tests/unit/streaming/test_streaming_group_by.py
+++ b/py-polars/tests/unit/streaming/test_streaming_group_by.py
@@ -8,6 +8,7 @@
 
 import polars as pl
 from polars.testing import assert_frame_equal
+from polars.testing._constants import PARTITION_LIMIT
 
 if TYPE_CHECKING:
     from pathlib import Path
@@ -480,3 +481,10 @@ def test_streaming_groupby_binary_15116() -> None:
         "str": [b"A", b"BB", b"CCCC", b"DDDDDDDD", b"EEEEEEEEEEEEEEEE"],
         "count": [3, 2, 2, 2, 1],
     }
+
+
+def test_streaming_group_by_convert_15380() -> None:
+    assert (
+        pl.DataFrame({"a": [1] * PARTITION_LIMIT}).group_by(b="a").len()["len"].item()
+        == PARTITION_LIMIT
+    )