diff --git a/table/full_filter_block.cc b/table/full_filter_block.cc
index 4af3125ba..0e621042d 100644
--- a/table/full_filter_block.cc
+++ b/table/full_filter_block.cc
@@ -17,6 +17,8 @@ FullFilterBlockBuilder::FullFilterBlockBuilder(
     FilterBitsBuilder* filter_bits_builder)
     : prefix_extractor_(prefix_extractor),
       whole_key_filtering_(whole_key_filtering),
+      last_whole_key_recorded_(false),
+      last_prefix_recorded_(false),
       num_added_(0) {
   assert(filter_bits_builder != nullptr);
   filter_bits_builder_.reset(filter_bits_builder);
@@ -33,9 +35,10 @@ void FullFilterBlockBuilder::Add(const Slice& key) {
       // bits builder to properly detect the duplicates by comparing with the
       // last item.
       Slice last_whole_key = Slice(last_whole_key_str_);
-      if (last_whole_key.compare(key) != 0) {
+      if (!last_whole_key_recorded_ || last_whole_key.compare(key) != 0) {
         AddKey(key);
-        last_whole_key_str_ = key.ToString();
+        last_whole_key_recorded_ = true;
+        last_whole_key_str_.assign(key.data(), key.size());
       }
     }
   }
@@ -59,9 +62,10 @@ inline void FullFilterBlockBuilder::AddPrefix(const Slice& key) {
     // bits builder to properly detect the duplicates by comparing with the last
     // item.
     Slice last_prefix = Slice(last_prefix_str_);
-    if (last_prefix.compare(prefix) != 0) {
+    if (!last_prefix_recorded_ || last_prefix.compare(prefix) != 0) {
       AddKey(prefix);
-      last_prefix_str_ = prefix.ToString();
+      last_prefix_recorded_ = true;
+      last_prefix_str_.assign(prefix.data(), prefix.size());
     }
   } else {
     AddKey(prefix);
diff --git a/table/full_filter_block.h b/table/full_filter_block.h
index eb2703a4d..352051052 100644
--- a/table/full_filter_block.h
+++ b/table/full_filter_block.h
@@ -59,7 +59,9 @@ class FullFilterBlockBuilder : public FilterBlockBuilder {
   // should NOT dereference them.
   const SliceTransform* prefix_extractor_;
   bool whole_key_filtering_;
+  bool last_whole_key_recorded_;
   std::string last_whole_key_str_;
+  bool last_prefix_recorded_;
   std::string last_prefix_str_;
 
   uint32_t num_added_;
diff --git a/table/full_filter_block_test.cc b/table/full_filter_block_test.cc
index 73541264a..eb77ec056 100644
--- a/table/full_filter_block_test.cc
+++ b/table/full_filter_block_test.cc
@@ -162,6 +162,20 @@ TEST_F(FullFilterBlockTest, EmptyBuilder) {
 }
 
 TEST_F(FullFilterBlockTest, DuplicateEntries) {
+  {  // empty prefixes
+    std::unique_ptr<const SliceTransform> prefix_extractor(
+        NewFixedPrefixTransform(0));
+    auto bits_builder = dynamic_cast<FullFilterBitsBuilder*>(
+        table_options_.filter_policy->GetFilterBitsBuilder());
+    const bool WHOLE_KEY = true;
+    FullFilterBlockBuilder builder(prefix_extractor.get(), WHOLE_KEY,
+                                   bits_builder);
+    ASSERT_EQ(0, builder.NumAdded());
+    builder.Add("key");  // test with empty prefix
+    ASSERT_EQ(2, bits_builder->hash_entries_.size());
+  }
+
+  // mix of empty and non-empty
   std::unique_ptr<const SliceTransform> prefix_extractor(
       NewFixedPrefixTransform(7));
   auto bits_builder = dynamic_cast<FullFilterBitsBuilder*>(
@@ -170,13 +184,14 @@ TEST_F(FullFilterBlockTest, DuplicateEntries) {
   FullFilterBlockBuilder builder(prefix_extractor.get(), WHOLE_KEY,
                                  bits_builder);
   ASSERT_EQ(0, builder.NumAdded());
+  builder.Add("");  // test with empty key too
   builder.Add("prefix1key1");
   builder.Add("prefix1key1");
   builder.Add("prefix1key2");
   builder.Add("prefix1key3");
   builder.Add("prefix2key4");
   // two prefix adn 4 keys
-  ASSERT_EQ(2 + 4, bits_builder->hash_entries_.size());
+  ASSERT_EQ(1 + 2 + 4, bits_builder->hash_entries_.size());
 }
 
 TEST_F(FullFilterBlockTest, SingleChunk) {