diff --git a/hphp/runtime/ext/thrift/binary.cpp b/hphp/runtime/ext/thrift/binary.cpp
index 9a1e0bbcb66e6..d86b17500dceb 100644
--- a/hphp/runtime/ext/thrift/binary.cpp
+++ b/hphp/runtime/ext/thrift/binary.cpp
@@ -176,7 +176,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
       auto const& val_spec = fieldspec.val();
       hasTypeWrapper = hasTypeWrapper || val_spec.isTypeWrapped;
       if (s_harray.equal(fieldspec.format)) {
-        DictInit arr(get_initial_array_size(size));
+        DictInit arr(size);
         for (uint32_t i = 0; i < size; i++) {
           switch (types[0]) {
             case TType::T_I08:
@@ -208,7 +208,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
         }
         return arr.toVariant();
       } else if (s_collection.equal(fieldspec.format)) {
-        auto obj(req::make<c_Map>(get_initial_array_size(size)));
+        auto obj(req::make<c_Map>(size));
         for (uint32_t s = 0; s < size; ++s) {
           auto key = binary_deserialize(
             types[0], transport, key_spec, options, hasTypeWrapper);
@@ -218,7 +218,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
         }
         return Variant(std::move(obj));
       } else {
-        DictInit arr(get_initial_array_size(size));
+        DictInit arr(size);
         if (options & k_THRIFT_MARK_LEGACY_ARRAYS) {
           arr.setLegacyArray();
         }
@@ -250,7 +250,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
         if (size == 0) {
           return Variant(req::make<c_Vector>());
         }
-        auto vec = req::make<c_Vector>(get_initial_array_size(size));
+        auto vec = req::make<c_Vector>(size);
         int64_t i = 0;
         do {
           auto val = binary_deserialize(
@@ -280,7 +280,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
       check_container_size(size);
       auto const& val_spec = fieldspec.val();
       if (s_harray.equal(fieldspec.format)) {
-        KeysetInit arr(get_initial_array_size(size));
+        KeysetInit arr(size);
         for (uint32_t i = 0; i < size; i++) {
           arr.add(
             binary_deserialize(type, transport, val_spec, options, hasTypeWrapper)
@@ -288,7 +288,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
         }
         return arr.toVariant();
       } else if (s_collection.equal(fieldspec.format)) {
-        auto set_ret(req::make<c_Set>(get_initial_array_size(size)));
+        auto set_ret(req::make<c_Set>(size));
         for (uint32_t s = 0; s < size; ++s) {
           Variant key = binary_deserialize(
             type, transport, val_spec, options, hasTypeWrapper);
@@ -301,7 +301,7 @@ Variant binary_deserialize_internal(int8_t thrift_typeID,
 
         return Variant(std::move(set_ret));
       } else {
-        DictInit init(get_initial_array_size(size));
+        DictInit init(size);
         if (options & k_THRIFT_MARK_LEGACY_ARRAYS) {
           init.setLegacyArray();
         }
diff --git a/hphp/runtime/ext/thrift/compact.cpp b/hphp/runtime/ext/thrift/compact.cpp
index 2f54cabbea1ef..91c9e4b448d09 100644
--- a/hphp/runtime/ext/thrift/compact.cpp
+++ b/hphp/runtime/ext/thrift/compact.cpp
@@ -1118,7 +1118,7 @@ struct CompactReader {
       const uint32_t size,
       bool& hasTypeWrapper
     ) {
-      DictInit arr(get_initial_array_size(size));
+      DictInit arr(size);
       switch (keyType) {
         case TType::T_I08:
         case TType::T_I16:
@@ -1163,7 +1163,7 @@ struct CompactReader {
       const uint32_t size,
       bool& hasTypeWrapper
     ) {
-      auto map(req::make<c_Map>(get_initial_array_size(size)));
+      auto map(req::make<c_Map>(size));
       if (spec.key().adapter == nullptr && spec.val().adapter == nullptr &&
           typeIs16to64Int(keyType) && typeIs16to64Int(valueType)) {
         hasTypeWrapper = hasTypeWrapper || spec.key().isTypeWrapped || spec.val().isTypeWrapped;
@@ -1190,7 +1190,7 @@ struct CompactReader {
       } else if (s_collection.equal(spec.format)) {
         return readMapCollection(spec, keyType, valueType, size, hasTypeWrapper);
       } else {
-        DictInit arr(get_initial_array_size(size));
+        DictInit arr(size);
         if (options & k_THRIFT_MARK_LEGACY_ARRAYS) {
           arr.setLegacyArray();
         }
@@ -1260,7 +1260,7 @@ struct CompactReader {
         readCollectionEnd();
         return Variant(req::make<c_Vector>());
       }
-      auto vec = req::make<c_Vector>(get_initial_array_size(size));
+      auto vec = req::make<c_Vector>(size);
       if (spec.val().adapter == nullptr && typeIs16to64Int(valueType)) {
         readIntList(
           [&, i = 0LL](int64_t val) mutable {
@@ -1307,14 +1307,14 @@ struct CompactReader {
       readListBegin(valueType, size);
 
       if (s_harray.equal(spec.format)) {
-        KeysetInit arr(get_initial_array_size(size));
+        KeysetInit arr(size);
         for (uint32_t i = 0; i < size; i++) {
           arr.add(readField(spec.val(), valueType, hasTypeWrapper));
         }
         readCollectionEnd();
         return arr.toVariant();
       } else if (s_collection.equal(spec.format)) {
-        auto set_ret = req::make<c_Set>(get_initial_array_size(size));
+        auto set_ret = req::make<c_Set>(size);
         for (uint32_t i = 0; i < size; i++) {
           Variant value = readField(spec.val(), valueType, hasTypeWrapper);
           set_ret->add(value);
@@ -1322,7 +1322,7 @@ struct CompactReader {
         readCollectionEnd();
         return Variant(std::move(set_ret));
       } else {
-        DictInit ainit(get_initial_array_size(size));
+        DictInit ainit(size);
         if (options & k_THRIFT_MARK_LEGACY_ARRAYS) {
           ainit.setLegacyArray();
         }
diff --git a/hphp/runtime/ext/thrift/util.h b/hphp/runtime/ext/thrift/util.h
index 370eda797f08e..85d2cc53af55a 100644
--- a/hphp/runtime/ext/thrift/util.h
+++ b/hphp/runtime/ext/thrift/util.h
@@ -79,15 +79,11 @@ inline bool is_value_type_default(int8_t thrift_typeID, const Variant& value) {
     }
 }
 
-inline uint32_t get_initial_array_size(const uint32_t size) {
+inline Array initialize_array(const uint32_t size) {
   // Reserve up to 16k entries for perf - but after that use "normal"
   // array expansion so that we ensure the data is actually there before
   // allocating massive arrays.
-  return std::min(16384u, size);
-}
-
-inline Array initialize_array(const uint32_t size) {
- return Array::attach(VanillaVec::MakeReserveVec(get_initial_array_size(size)));
+  return Array::attach(VanillaVec::MakeReserveVec(std::min(16384u, size)));
 }
 
 inline void check_container_size(const uint32_t size) {