diff --git a/libstdc++-v3/include/bits/functional_hash.h b/libstdc++-v3/include/bits/functional_hash.h
index c00113eff83..292c0ee03f7 100644
--- a/libstdc++-v3/include/bits/functional_hash.h
+++ b/libstdc++-v3/include/bits/functional_hash.h
@@ -280,10 +280,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// @} group hashes
 
-  // Hint about performance of hash functor. If not fast the hash-based
-  // containers will cache the hash code.
-  // Default behavior is to consider that hashers are fast unless specified
-  // otherwise.
+  /** Hint about performance of hash functions.
+   *
+   * If a given hash function object is not fast, the hash-based containers
+   * will cache the hash code.
+   * The default behavior is to consider that hashers are fast unless specified
+   * otherwise.
+   *
+   * Users can specialize this for their own hash functions in order to force
+   * caching of hash codes in unordered containers. Specializing this trait
+   * affects the ABI of the unordered containers, so use it carefully.
+   */
   template<typename _Hash>
     struct __is_fast_hash : public std::true_type
     { };
diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index edc151ef15b..29ec1192f32 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -34,11 +34,10 @@
 
 #include <bits/hashtable_policy.h>
 #include <bits/enable_special_members.h>
+#include <bits/stl_function.h> // __has_is_transparent_t
 #if __cplusplus > 201402L
 # include <bits/node_handle.h>
 #endif
-#include <bits/functional_hash.h>
-#include <bits/stl_function.h> // equal_to, _Identity, _Select1st
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index 799c3e986b4..1a259702f98 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -32,7 +32,9 @@
 #define _HASHTABLE_POLICY_H 1
 
 #include <tuple>		// for std::tuple, std::forward_as_tuple
+#include <bits/functional_hash.h> // for __is_fast_hash
 #include <bits/stl_algobase.h>	// for std::min, std::is_permutation.
+#include <bits/stl_pair.h>	// for std::pair
 #include <ext/aligned_buffer.h>	// for __gnu_cxx::__aligned_buffer
 #include <ext/alloc_traits.h>	// for std::__alloc_rebind
 #include <ext/numeric_traits.h>	// for __gnu_cxx::__int_traits
diff --git a/libstdc++-v3/include/bits/unordered_map.h b/libstdc++-v3/include/bits/unordered_map.h
index d5edfde8caf..5a3e6f61af2 100644
--- a/libstdc++-v3/include/bits/unordered_map.h
+++ b/libstdc++-v3/include/bits/unordered_map.h
@@ -30,6 +30,11 @@
 #ifndef _UNORDERED_MAP_H
 #define _UNORDERED_MAP_H
 
+#include <bits/hashtable.h>
+#include <bits/allocator.h>
+#include <bits/functional_hash.h> // hash
+#include <bits/stl_function.h>    // equal_to
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
diff --git a/libstdc++-v3/include/bits/unordered_set.h b/libstdc++-v3/include/bits/unordered_set.h
index d2fa2c51171..740bbafd4c9 100644
--- a/libstdc++-v3/include/bits/unordered_set.h
+++ b/libstdc++-v3/include/bits/unordered_set.h
@@ -30,6 +30,11 @@
 #ifndef _UNORDERED_SET_H
 #define _UNORDERED_SET_H
 
+#include <bits/hashtable.h>
+#include <bits/allocator.h>
+#include <bits/functional_hash.h> // hash
+#include <bits/stl_function.h>    // equal_to
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
diff --git a/libstdc++-v3/include/std/unordered_map b/libstdc++-v3/include/std/unordered_map
index e13bb9a2148..b50ec2a8de2 100644
--- a/libstdc++-v3/include/std/unordered_map
+++ b/libstdc++-v3/include/std/unordered_map
@@ -35,15 +35,7 @@
 # include <bits/c++0x_warning.h>
 #else
 
-#include <type_traits>
 #include <initializer_list>
-#include <bits/allocator.h>
-#include <ext/alloc_traits.h>
-#include <ext/aligned_buffer.h>
-#include <bits/stl_pair.h>
-#include <bits/stl_function.h> // equal_to, _Identity, _Select1st
-#include <bits/functional_hash.h>
-#include <bits/hashtable.h>
 #include <bits/unordered_map.h>
 #include <bits/range_access.h>
 #include <bits/erase_if.h>
diff --git a/libstdc++-v3/include/std/unordered_set b/libstdc++-v3/include/std/unordered_set
index 8b665718a83..edaa517635b 100644
--- a/libstdc++-v3/include/std/unordered_set
+++ b/libstdc++-v3/include/std/unordered_set
@@ -35,15 +35,7 @@
 # include <bits/c++0x_warning.h>
 #else
 
-#include <type_traits>
 #include <initializer_list>
-#include <bits/allocator.h>
-#include <ext/alloc_traits.h>
-#include <ext/aligned_buffer.h>
-#include <bits/stl_pair.h>
-#include <bits/stl_function.h> // equal_to, _Identity, _Select1st
-#include <bits/functional_hash.h>
-#include <bits/hashtable.h>
 #include <bits/unordered_set.h>
 #include <bits/range_access.h>
 #include <bits/erase_if.h>