diff --git a/README.md b/README.md
index 7b8392c..1f02fbe 100644
--- a/README.md
+++ b/README.md
@@ -21,7 +21,7 @@ This repository aims to provide a set of excellent **hash map** implementations,
 
 - Easy to **forward declare**: just include `phmap_fwd_decl.h` in your header files to forward declare Parallel Hashmap containers [note: this does not work currently for hash maps with pointer keys]
 
-- **Dump/load** feature: when a hash map stores data that is `std::trivially_copyable`, the table can be dumped to disk and restored as a single array, very efficiently, and without requiring any hash computation. This is typically about 10 times faster than doing element-wise serialization to disk, but it will use 10% to 60% extra disk space. See `examples/serialize.cc`. _(hash map/set only)_
+- **Dump/load** feature: when a `flat` hash map stores data that is `std::trivially_copyable`, the table can be dumped to disk and restored as a single array, very efficiently, and without requiring any hash computation. This is typically about 10 times faster than doing element-wise serialization to disk, but it will use 10% to 60% extra disk space. See `examples/serialize.cc`. _(flat hash map/set only)_
 
 - **Tested** on Windows (vs2015 & vs2017, vs2019, Intel compiler 18 and 19), linux (g++ 4.8.4, 5, 6, 7, 8, clang++ 3.9, 4.0, 5.0) and MacOS (g++ and clang++) - click on travis and appveyor icons above for detailed test status.
 
diff --git a/parallel_hashmap/btree.h b/parallel_hashmap/btree.h
index 0cb44a4..7c73162 100644
--- a/parallel_hashmap/btree.h
+++ b/parallel_hashmap/btree.h
@@ -54,25 +54,12 @@
     #pragma warning(disable : 5045) // Compiler will insert Spectre mitigation for memory load if /Qspectre switch specified
 #endif
 
-#include <initializer_list>
-#include <iterator>
-#include <utility>
 
-#include <algorithm>
-#include <cassert>
-#include <cstddef>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
-#include <functional>
-#include <iterator>
 #include <limits>
 #include <new>
-#include <string>
-#include <type_traits>
-#include <utility>
-#include <initializer_list>
-#include <iterator>
 
 #include "phmap_fwd_decl.h"
 #include "phmap_base.h"
diff --git a/parallel_hashmap/phmap.h b/parallel_hashmap/phmap.h
index 630dfee..880938b 100644
--- a/parallel_hashmap/phmap.h
+++ b/parallel_hashmap/phmap.h
@@ -3434,6 +3434,8 @@ public:
         return modify_if_impl<K, F, Lockable::UniqueLock>(key, std::forward<F>(f));
     }
 
+    
+
     template <class K = key_type, class P = Policy, K* = nullptr>
     MappedReference<P> operator[](key_arg<K>&& key) {
         return Policy::value(&*try_emplace(std::forward<K>(key)).first);
diff --git a/tests/parallel_hash_map_test.cc b/tests/parallel_hash_map_test.cc
index fcac843..48241eb 100644
--- a/tests/parallel_hash_map_test.cc
+++ b/tests/parallel_hash_map_test.cc
@@ -13,13 +13,20 @@ TEST(THIS_TEST_NAME, ThreadSafeContains) {
     // We can't test mutable keys, or non-copyable keys with ThisMap.
     // Test that the nodes have the proper API.
     ThisMap<int, int> m = { {1, 7}, {2, 9} };
-    auto val = 0;
-
-    auto func = [&val](int& v) { val = v; };
-    EXPECT_TRUE(m.if_contains(2, func));
+    const ThisMap<int, int>& const_m(m);
+    
+    auto val = 0; 
+    auto get_value = [&val](const int& v) { val = v; };
+    EXPECT_TRUE(const_m.if_contains(2, get_value));
     EXPECT_EQ(val, 9);
 
-    EXPECT_FALSE(m.if_contains(3, func));
+    EXPECT_FALSE(m.if_contains(3, get_value));
+
+    auto set_value = [&val](int& v) { v = 11; };
+    EXPECT_TRUE(m. modify_if(2, set_value));
+    EXPECT_EQ(m[2], 11);
+
+    EXPECT_FALSE(m.modify_if(3, set_value));
 }
 
 }  // namespace