diff --git a/pyterrier_dr/flex/np_retr.py b/pyterrier_dr/flex/np_retr.py
index ff9a21d..27a65d0 100644
--- a/pyterrier_dr/flex/np_retr.py
+++ b/pyterrier_dr/flex/np_retr.py
@@ -6,16 +6,19 @@
 from ..indexes import RankedLists
 from . import FlexIndex
 import ir_datasets
+import pyterrier_alpha as pta
 
 logger = ir_datasets.log.easy()
 
 class NumpyRetriever(pt.Transformer):
-    def __init__(self, flex_index, num_results=1000, batch_size=None):
+    def __init__(self, flex_index, num_results=1000, batch_size=None, drop_query_vec=False):
         self.flex_index = flex_index
         self.num_results = num_results
         self.batch_size = batch_size or 4096
+        self.drop_query_vec = drop_query_vec
 
     def transform(self, inp: pd.DataFrame) -> pd.DataFrame:
+        pta.validate.query_frame(inp, extra_columns=['query_vec'])
         inp = inp.reset_index(drop=True)
         query_vecs = np.stack(inp['query_vec'])
         docnos, dvecs, config = self.flex_index.payload()
@@ -37,19 +40,19 @@ def transform(self, inp: pd.DataFrame) -> pd.DataFrame:
             scores = query_vecs @ doc_batch
             dids = np.arange(idx_start, idx_start+doc_batch.shape[1], dtype='i4').reshape(1, -1).repeat(num_q, axis=0)
             ranked_lists.update(scores, dids)
-        result_scores, result_dids = ranked_lists.results()
-        result_docnos = docnos.fwd[result_dids]
-        cols = {
-            'score': np.concatenate(result_scores),
-            'docno': np.concatenate(result_docnos),
-            'docid': np.concatenate(result_dids),
-            'rank': np.concatenate([np.arange(len(scores)) for scores in result_scores]),
-        }
-        idxs = list(itertools.chain(*(itertools.repeat(i, len(scores)) for i, scores in enumerate(result_scores))))
-        for col in inp.columns:
-            if col != 'query_vec':
-                cols[col] = inp[col][idxs].values
-        return pd.DataFrame(cols)
+
+        result = pta.DataFrameBuilder(['score', 'docno', 'docid', 'rank'])
+        for scores, dids in zip(*ranked_lists.results()):
+            result.extend({
+                'score': scores,
+                'docno': docnos.fwd[dids],
+                'docid': dids,
+                'rank': np.arange(len(scores)),
+            })
+
+        if self.drop_query_vec:
+            inp = inp.drop(columns='query_vec')
+        return result.to_df(inp)
 
 
 class NumpyVectorLoader(pt.Transformer):
@@ -108,18 +111,18 @@ def transform(self, inp):
         return res
 
 
-def _np_retriever(self, num_results=1000, batch_size=None):
-        return NumpyRetriever(self, num_results=num_results, batch_size=batch_size)
+def _np_retriever(self, num_results=1000, batch_size=None, drop_query_vec=False):
+    return NumpyRetriever(self, num_results=num_results, batch_size=batch_size, drop_query_vec=drop_query_vec)
 FlexIndex.np_retriever = _np_retriever
 
 
 def _np_vec_loader(self):
-        return NumpyVectorLoader(self)
+    return NumpyVectorLoader(self)
 FlexIndex.np_vec_loader = _np_vec_loader
 FlexIndex.vec_loader = _np_vec_loader # default vec_loader
 
 
 def _np_scorer(self, num_results=None):
-        return NumpyScorer(self, num_results)
+    return NumpyScorer(self, num_results)
 FlexIndex.np_scorer = _np_scorer
 FlexIndex.scorer = _np_scorer # default scorer
diff --git a/tests/test_flexindex.py b/tests/test_flexindex.py
index 9d5e99b..952ae01 100644
--- a/tests/test_flexindex.py
+++ b/tests/test_flexindex.py
@@ -1,3 +1,4 @@
+import functools
 import tempfile
 import unittest
 import numpy as np
@@ -129,6 +130,9 @@ def test_scann_retriever(self):
     def test_np_retriever(self):
         self._test_retr(FlexIndex.np_retriever)
 
+    def test_np_retriever_drop_query_vec(self):
+        self._test_retr(functools.partial(FlexIndex.np_retriever, drop_query_vec=True))
+
     def test_torch_retriever(self):
         self._test_retr(FlexIndex.torch_retriever)