diff --git a/src/function/list_group.cc b/src/function/list_group.cc
index 70f9460..c577528 100644
--- a/src/function/list_group.cc
+++ b/src/function/list_group.cc
@@ -34,7 +34,7 @@ U32ListStruct GroupIndex(KList keys, void *exec_context) {
   result.data = reinterpret_cast<uint32_t *>(exec_ctx->arena.Allocate(sizeof(uint32_t) * keys.len));
 
   std::unordered_map<typename KList::CElementType, uint32_t> table;
-  table.reserve(keys.len * 2);
+  table.reserve(keys.len);
   uint32_t next_id = 0;
   for (uint32_t i = 0; i < keys.len; ++i) {
     auto [it, inserted] = table.try_emplace(keys.data[i], next_id);
@@ -53,7 +53,7 @@ U32ListStruct GroupIndexString(StringListStruct keys, void *exec_context) {
   result.data = reinterpret_cast<uint32_t *>(exec_ctx->arena.Allocate(sizeof(uint32_t) * keys.len));
 
   std::unordered_map<std::string_view, uint32_t> table;
-  table.reserve(static_cast<size_t>(keys.len) * 2);
+  table.reserve(static_cast<size_t>(keys.len));
   uint32_t next_id = 0;
   for (uint32_t i = 0; i < keys.len; ++i) {
     std::string_view sv(keys.data[i].data, keys.data[i].len);
diff --git a/src/function/list_indexing.cc b/src/function/list_indexing.cc
index 39318a6..f92262c 100644
--- a/src/function/list_indexing.cc
+++ b/src/function/list_indexing.cc
@@ -31,7 +31,7 @@ template <typename KList>
 void *BuildLookupTableInt(KList b, void *exec_context) {
   auto *exec_ctx = reinterpret_cast<ExecContext *>(exec_context);
   IntLookupTable<KList> seed;
-  seed.reserve(static_cast<size_t>(b.len) * 2);
+  seed.reserve(static_cast<size_t>(b.len));
   for (uint32_t j = 0; j < b.len; ++j) {
     seed.try_emplace(b.data[j], j);
   }
@@ -41,7 +41,7 @@ void *BuildLookupTableInt(KList b, void *exec_context) {
 void *BuildLookupTableString(StringListStruct b, void *exec_context) {
   auto *exec_ctx = reinterpret_cast<ExecContext *>(exec_context);
   StringLookupTable seed;
-  seed.reserve(static_cast<size_t>(b.len) * 2);
+  seed.reserve(static_cast<size_t>(b.len));
   for (uint32_t j = 0; j < b.len; ++j) {
     std::string_view sv(b.data[j].data, b.data[j].len);
     seed.try_emplace(sv, j);