diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -47,6 +47,7 @@
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Sema/IdentifierResolver.h"
+#include "clang/Sema/Sema.h"
 #include "clang/Serialization/ASTBitCodes.h"
 #include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/ContinuousRangeMap.h"
@@ -3195,6 +3196,9 @@
     // Add the declaration to its redeclaration context so later merging
     // lookups will find it.
     MergeDC->makeDeclVisibleInContextImpl(New, /*Internal*/true);
+    if (isa<NamespaceDecl>(New) && Name.getAsString() == "std")
+      if (!Reader.getSema()->StdNamespace)
+        Reader.getSema()->StdNamespace = New;
   }
 }
 
@@ -3358,6 +3362,14 @@
           return FindExistingResult(Reader, D, Existing, AnonymousDeclNumber,
                                     TypedefNameForLinkage);
     }
+    if (isa<NamespaceDecl>(D) && D->getName() == "std") {
+      auto StdPtr = Reader.getSema()->StdNamespace;
+      if (StdPtr.isValid() && !StdPtr.isOffset())
+        if (auto *Std = cast_or_null<NamespaceDecl>(StdPtr.get(nullptr)))
+          if (isSameEntity(Std, D))
+            return FindExistingResult(Reader, D, Std, AnonymousDeclNumber,
+                                      TypedefNameForLinkage);
+    }
   } else {
     // Not in a mergeable context.
     return FindExistingResult(Reader);
diff --git a/clang/test/Modules/Inputs/pr39287-2/a.h b/clang/test/Modules/Inputs/pr39287-2/a.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/pr39287-2/a.h
@@ -0,0 +1 @@
+namespace std { class type_info; }
diff --git a/clang/test/Modules/Inputs/pr39287-2/module.modulemap b/clang/test/Modules/Inputs/pr39287-2/module.modulemap
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/pr39287-2/module.modulemap
@@ -0,0 +1,3 @@
+module "a.h" {
+  header "a.h"
+}
diff --git a/clang/test/Modules/Inputs/pr39287/a.h b/clang/test/Modules/Inputs/pr39287/a.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/pr39287/a.h
@@ -0,0 +1 @@
+namespace std {}
diff --git a/clang/test/Modules/Inputs/pr39287/module.modulemap b/clang/test/Modules/Inputs/pr39287/module.modulemap
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/pr39287/module.modulemap
@@ -0,0 +1,3 @@
+module "a.h" {
+  header "a.h"
+}
diff --git a/clang/test/Modules/pr39287-2.cpp b/clang/test/Modules/pr39287-2.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/pr39287-2.cpp
@@ -0,0 +1,12 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -std=c++17 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs/pr39287-2 %s -verify
+
+class A {
+  virtual ~A() {}
+};
+
+#include "a.h"
+
+void foo() {
+  typeid(foo); // expected-warning {{expression result unused}}
+}
diff --git a/clang/test/Modules/pr39287.cpp b/clang/test/Modules/pr39287.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/pr39287.cpp
@@ -0,0 +1,14 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -std=c++17 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs/pr39287 %s -verify
+
+class A {
+  virtual ~A() {}
+};
+
+#include "a.h"
+
+namespace std { class type_info; }
+
+void foo() {
+  typeid(foo); // expected-warning {{expression result unused}}
+}