diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -6674,8 +6674,15 @@
       } else if (Steps.size() == 1) {
         bool MaybeQ1 = Q1.isAddressSpaceSupersetOf(Q2);
         bool MaybeQ2 = Q2.isAddressSpaceSupersetOf(Q1);
-        if (MaybeQ1 == MaybeQ2)
-          return QualType(); // No unique best address space.
+        if (MaybeQ1 == MaybeQ2) {
+          // Exception for ptr size address spaces. Should be able to choose
+          // either address space during comparison.
+          if (isPtrSizeAddressSpace(Q1.getAddressSpace()) ||
+              isPtrSizeAddressSpace(Q2.getAddressSpace()))
+            MaybeQ1 = true;
+          else
+            return QualType(); // No unique best address space.
+        }
         Quals.setAddressSpace(MaybeQ1 ? Q1.getAddressSpace()
                                       : Q2.getAddressSpace());
       } else {
diff --git a/clang/test/Sema/MicrosoftExtensions.cpp b/clang/test/Sema/MicrosoftExtensions.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/MicrosoftExtensions.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple i686-windows %s -fsyntax-only -Wmicrosoft -verify -fms-extensions
+// RUN: %clang_cc1 -triple x86_64-windows %s -fsyntax-only -Wmicrosoft -verify -fms-extensions
+// expected-no-diagnostics
+
+// Check that __ptr32/__ptr64 can be compared.
+int test_ptr_comparison(int * __ptr32 __uptr p32u, int * __ptr32 __sptr p32s,
+                         int * __ptr64 p64) {
+  return (p32u == p32s) +
+         (p32u == p64) +
+         (p32s == p64);
+}