diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 93293c0631a..35be45e4e46 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,12 @@
+2018-10-12  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/77691
+	* include/experimental/memory_resource (__resource_adaptor_imp): Do
+	not allocate sizes smaller than alignment when relying on guaranteed
+	alignment.
+	* testsuite/experimental/memory_resource/new_delete_resource.cc:
+	Adjust expected number of bytes allocated for alignof(max_align_t).
+
 2018-10-11  François Dumont  <fdumont@gcc.gnu.org>
 
 	* include/debug/forward_list
diff --git a/libstdc++-v3/include/experimental/memory_resource b/libstdc++-v3/include/experimental/memory_resource
index ccb45bfa335..fd40d2cf45b 100644
--- a/libstdc++-v3/include/experimental/memory_resource
+++ b/libstdc++-v3/include/experimental/memory_resource
@@ -421,7 +421,12 @@ namespace pmr {
       do_allocate(size_t __bytes, size_t __alignment) override
       {
 	if (__alignment <= __guaranteed_alignment<_Alloc>::value)
-	  return _M_alloc.allocate(__bytes);
+	  {
+	    if (__bytes < __alignment)
+	      __bytes = __alignment;
+	    return _M_alloc.allocate(__bytes);
+	  }
+
 
 	const _AlignMgr __mgr(__bytes, __alignment);
 	// Assume _M_alloc returns 1-byte aligned memory, so allocate enough
@@ -437,6 +442,8 @@ namespace pmr {
 	auto __ptr = static_cast<char*>(__p);
 	if (__alignment <= __guaranteed_alignment<_Alloc>::value)
 	  {
+	    if (__bytes < __alignment)
+	      __bytes = __alignment;
 	    _M_alloc.deallocate(__ptr, __bytes);
 	    return;
 	  }
diff --git a/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc b/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
index 11667b1d138..3af3861d1a0 100644
--- a/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
+++ b/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
@@ -109,11 +109,13 @@ test03()
   using std::size_t;
   void* p = nullptr;
 
+  auto max = [](int n, int a) { return n > a ? n : a; };
+
   bytes_allocated = 0;
 
   memory_resource* r1 = new_delete_resource();
-  p = r1->allocate(1);
-  VERIFY( bytes_allocated == 1 );
+  p = r1->allocate(1); // uses alignment = alignof(max_align_t)
+  VERIFY( bytes_allocated <= alignof(max_align_t) );
   VERIFY( aligned<max_align_t>(p) );
   r1->deallocate(p, 1);
   VERIFY( bytes_allocated == 0 );
@@ -125,13 +127,13 @@ test03()
   VERIFY( bytes_allocated == 0 );
 
   p = r1->allocate(3, alignof(short));
-  VERIFY( bytes_allocated == 3 );
+  VERIFY( bytes_allocated == max(3, alignof(short)) );
   VERIFY( aligned<short>(p) );
   r1->deallocate(p, 3, alignof(short));
   VERIFY( bytes_allocated == 0 );
 
   p = r1->allocate(4, alignof(long));
-  VERIFY( bytes_allocated == 4 );
+  VERIFY( bytes_allocated == max(4, alignof(long)) );
   VERIFY( aligned<long>(p) );
   r1->deallocate(p, 4, alignof(long));
   VERIFY( bytes_allocated == 0 );