diff --git a/crates/polars-core/src/chunked_array/builder/boolean.rs b/crates/polars-core/src/chunked_array/builder/boolean.rs
index 407bc3abcf53..7723802dd0ac 100644
--- a/crates/polars-core/src/chunked_array/builder/boolean.rs
+++ b/crates/polars-core/src/chunked_array/builder/boolean.rs
@@ -21,13 +21,14 @@ impl ChunkedBuilder<bool, BooleanType> for BooleanChunkedBuilder {
 
     fn finish(mut self) -> BooleanChunked {
         let arr = self.array_builder.as_box();
+        let length = arr.len() as IdxSize;
 
         let mut ca = ChunkedArray {
             field: Arc::new(self.field),
             chunks: vec![arr],
             phantom: PhantomData,
             bit_settings: Default::default(),
-            length: 0,
+            length,
             null_count: 0,
         };
         ca.compute_len();
diff --git a/crates/polars-lazy/src/physical_plan/planner/expr.rs b/crates/polars-lazy/src/physical_plan/planner/expr.rs
index 0e614c4cb683..f690bf63f4e6 100644
--- a/crates/polars-lazy/src/physical_plan/planner/expr.rs
+++ b/crates/polars-lazy/src/physical_plan/planner/expr.rs
@@ -603,10 +603,11 @@ where
 
     let mut iter = chunks.into_iter();
     let first = iter.next().unwrap();
-    let out = iter.fold(first, |mut acc, s| {
-        acc.append(&s).unwrap();
+    let dtype = first.dtype();
+    let out = iter.fold(first.to_physical_repr().into_owned(), |mut acc, s| {
+        acc.append(&s.to_physical_repr()).unwrap();
         acc
     });
 
-    f(out).map(Some)
+    unsafe { f(out.cast_unchecked(&dtype).unwrap()).map(Some) }
 }