diff --git a/vortex-array/src/builders/list.rs b/vortex-array/src/builders/list.rs
index 91fcb8d0e..f93445e1c 100644
--- a/vortex-array/src/builders/list.rs
+++ b/vortex-array/src/builders/list.rs
@@ -34,7 +34,7 @@ where
     ) -> Self {
         // I would expect the list to have more than one value per index
         let value_builder = builder_with_capacity(value_dtype.as_ref(), 2 * capacity);
-        let mut index_builder = PrimitiveBuilder::with_capacity(nullability, capacity);
+        let mut index_builder = PrimitiveBuilder::with_capacity(Nullability::NonNullable, capacity);
 
         // The first index of the list, which is always 0 and represents an empty list.
         index_builder.append_zero();
diff --git a/vortex-array/src/builders/struct_.rs b/vortex-array/src/builders/struct_.rs
index 5ddb49eac..546d8296c 100644
--- a/vortex-array/src/builders/struct_.rs
+++ b/vortex-array/src/builders/struct_.rs
@@ -49,9 +49,10 @@ impl StructBuilder {
         }
 
         if let Some(fields) = struct_scalar.fields() {
-            for (builder, field) in self.builders.iter_mut().zip(fields) {
+            for (builder, field) in self.builders.iter_mut().zip_eq(fields) {
                 builder.append_scalar(&field)?;
             }
+            self.validity.append_value(true);
         } else {
             self.append_null()
         }
@@ -94,6 +95,7 @@ impl ArrayBuilder for StructBuilder {
     }
 
     fn finish(&mut self) -> VortexResult<ArrayData> {
+        let len = self.len();
         let fields: Vec<ArrayData> = self
             .builders
             .iter_mut()
@@ -105,12 +107,9 @@ impl ArrayBuilder for StructBuilder {
             Nullability::Nullable => Validity::Array(self.validity.finish()?),
         };
 
-        Ok(StructArray::try_new(
-            self.struct_dtype.names().clone(),
-            fields,
-            self.len(),
-            validity,
-        )?
-        .into_array())
+        Ok(
+            StructArray::try_new(self.struct_dtype.names().clone(), fields, len, validity)?
+                .into_array(),
+        )
     }
 }