diff --git a/db/db_impl.cc b/db/db_impl.cc
index e7f2abf99..12e07868f 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -3758,7 +3758,10 @@ Status DBImpl::GetDbIdentity(std::string& identity) {
 // Default implementations of convenience methods that subclasses of DB
 // can call if they wish
 Status DB::Put(const WriteOptions& opt, const Slice& key, const Slice& value) {
-  WriteBatch batch;
+  // Pre-allocate size of write batch conservatively.
+  // 8 bytes are taken by header, 4 bytes for count, 1 byte for type,
+  // and we allocate 11 extra bytes for key length, as well as value length.
+  WriteBatch batch(key.size() + value.size() + 24);
   batch.Put(key, value);
   return Write(opt, &batch);
 }
diff --git a/db/write_batch.cc b/db/write_batch.cc
index 2cfc8bd7d..7a6106afa 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -36,7 +36,8 @@ namespace rocksdb {
 // WriteBatch header has an 8-byte sequence number followed by a 4-byte count.
 static const size_t kHeader = 12;
 
-WriteBatch::WriteBatch() {
+WriteBatch::WriteBatch(size_t reserved_bytes) {
+  rep_.reserve((reserved_bytes > kHeader) ? reserved_bytes : kHeader);
   Clear();
 }
 
diff --git a/include/rocksdb/write_batch.h b/include/rocksdb/write_batch.h
index 30abead50..e7ce16005 100644
--- a/include/rocksdb/write_batch.h
+++ b/include/rocksdb/write_batch.h
@@ -35,7 +35,7 @@ struct SliceParts;
 
 class WriteBatch {
  public:
-  WriteBatch();
+  explicit WriteBatch(size_t reserved_bytes = 0);
   ~WriteBatch();
 
   // Store the mapping "key->value" in the database.