diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index a1d06b6fff1..57dde8c5533 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,13 @@
+2020-05-12  Jonathan Wakely  <jwakely@redhat.com>
+
+	Backport from mainline
+	2020-05-04  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/94906
+	* src/c++17/memory_resource.cc
+	(monotonic_buffer_resource::_Chunk::release): Use size_t for shift
+	operands.
+
 2020-05-07  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* config/abi/post/sparc64-linux-gnu/baseline_symbols.txt: Update.
diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc
index e28526d1bfe..f39360cb4bf 100644
--- a/libstdc++-v3/src/c++17/memory_resource.cc
+++ b/libstdc++-v3/src/c++17/memory_resource.cc
@@ -228,8 +228,8 @@ namespace pmr
 	  if (__ch->_M_canary != (__ch->_M_size | __ch->_M_align))
 	    return; // buffer overflow detected!
 
-	  size_t __size = (1u << __ch->_M_size);
-	  size_t __align = (1u << __ch->_M_align);
+	  size_t __size = (size_t)1 << __ch->_M_size;
+	  size_t __align = (size_t)1 << __ch->_M_align;
 	  void* __start = (char*)(__ch + 1) - __size;
 	  __r->deallocate(__start, __size, __align);
 	}