diff --git a/kv/storage/mem_storage.go b/kv/storage/mem_storage.go
index c6e56b50..38c054be 100644
--- a/kv/storage/mem_storage.go
+++ b/kv/storage/mem_storage.go
@@ -35,7 +35,7 @@ func (s *MemStorage) Stop() error {
 }
 
 func (s *MemStorage) Reader(ctx *kvrpcpb.Context) (StorageReader, error) {
-	return &memReader{s}, nil
+	return &memReader{s, 0}, nil
 }
 
 func (s *MemStorage) Write(ctx *kvrpcpb.Context, batch []Modify) error {
@@ -131,7 +131,8 @@ func (s *MemStorage) Len(cf string) int {
 
 // memReader is a StorageReader which reads from a MemStorage.
 type memReader struct {
-	inner *MemStorage
+	inner     *MemStorage
+	iterCount int
 }
 
 func (mr *memReader) GetCF(cf string, key []byte) ([]byte, error) {
@@ -168,18 +169,24 @@ func (mr *memReader) IterCF(cf string) engine_util.DBIterator {
 		return nil
 	}
 
+	mr.iterCount += 1
 	min := data.Min()
 	if min == nil {
-		return &memIter{data, memItem{}}
+		return &memIter{data, memItem{}, mr}
 	}
-	return &memIter{data, min.(memItem)}
+	return &memIter{data, min.(memItem), mr}
 }
 
-func (r *memReader) Close() {}
+func (r *memReader) Close() {
+	if r.iterCount > 0 {
+		panic("Unclosed iterator")
+	}
+}
 
 type memIter struct {
-	data *llrb.LLRB
-	item memItem
+	data   *llrb.LLRB
+	item   memItem
+	reader *memReader
 }
 
 func (it *memIter) Item() engine_util.DBItem {
@@ -212,7 +219,9 @@ func (it *memIter) Seek(key []byte) {
 	})
 }
 
-func (it *memIter) Close() {}
+func (it *memIter) Close() {
+	it.reader.iterCount -= 1
+}
 
 type memItem struct {
 	key   []byte