diff --git a/crates/polars-arrow/src/array/fixed_size_list/builder.rs b/crates/polars-arrow/src/array/fixed_size_list/builder.rs
index bff2151a6ef8..2be67595803f 100644
--- a/crates/polars-arrow/src/array/fixed_size_list/builder.rs
+++ b/crates/polars-arrow/src/array/fixed_size_list/builder.rs
@@ -32,7 +32,7 @@ impl<B: ArrayBuilder> StaticArrayBuilder for FixedSizeListArrayBuilder<B> {
     }
 
     fn reserve(&mut self, additional: usize) {
-        self.inner_builder.reserve(additional);
+        self.inner_builder.reserve(additional * self.size);
         self.validity.reserve(additional);
     }
 
diff --git a/crates/polars-arrow/src/array/fixed_size_list/mutable.rs b/crates/polars-arrow/src/array/fixed_size_list/mutable.rs
index 878a3b3d800a..9086e1f6eb26 100644
--- a/crates/polars-arrow/src/array/fixed_size_list/mutable.rs
+++ b/crates/polars-arrow/src/array/fixed_size_list/mutable.rs
@@ -136,7 +136,7 @@ impl<M: MutableArray> MutableFixedSizeListArray<M> {
 
     /// Reserves `additional` slots.
     pub fn reserve(&mut self, additional: usize) {
-        self.values.reserve(additional);
+        self.values.reserve(additional * self.size);
         if let Some(x) = self.validity.as_mut() {
             x.reserve(additional)
         }