diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -1335,6 +1335,16 @@
 
   /// \}
 
+  /// Mark the given module as affecting the current module or translation unit.
+  void markModuleAsAffecting(Module *M) {
+    if (!BuildingSubmoduleStack.empty()) {
+      if (M != BuildingSubmoduleStack.back().M)
+        BuildingSubmoduleStack.back().M->AffectingModules.insert(M);
+    } else {
+      AffectingModules.insert(M);
+    }
+  }
+
   /// Get the set of top-level modules that affected preprocessing, but were not
   /// imported.
   const llvm::SmallSetVector<Module *, 2> &getAffectingModules() const {
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -2014,8 +2014,7 @@
     // match Foo_Private and emit a warning asking for the user to write
     // @import Foo_Private instead. FIXME: remove this when existing clients
     // migrate off of Foo.Private syntax.
-    if (!Sub && PP->getLangOpts().ImplicitModules && Name == "Private" &&
-        Module == Module->getTopLevelModule()) {
+    if (!Sub && Name == "Private" && Module == Module->getTopLevelModule()) {
       SmallString<128> PrivateModule(Module->Name);
       PrivateModule.append("_Private");
 
@@ -2029,6 +2028,7 @@
         Sub = loadModule(ImportLoc, PrivPath, Visibility, IsInclusionDirective);
       if (Sub) {
         MapPrivateSubModToTopLevel = true;
+        getPreprocessor().markModuleAsAffecting(Module);
         if (!getDiagnostics().isIgnored(
                 diag::warn_no_priv_submodule_use_toplevel, ImportLoc)) {
           getDiagnostics().Report(Path[I].second,
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -2281,13 +2281,8 @@
     if (Imported) {
       Action = Import;
     } else if (Imported.isMissingExpected()) {
-      Module *M = static_cast<Module *>(Imported)->getTopLevelModule();
-      if (!BuildingSubmoduleStack.empty()) {
-        if (Imported != BuildingSubmoduleStack.back().M)
-          BuildingSubmoduleStack.back().M->AffectingModules.insert(M);
-      } else {
-        AffectingModules.insert(M);
-      }
+      markModuleAsAffecting(
+          static_cast<Module *>(Imported)->getTopLevelModule());
       // We failed to find a submodule that we assumed would exist (because it
       // was in the directory of an umbrella header, for instance), but no
       // actual module containing it exists (because the umbrella header is
diff --git a/clang/test/Modules/implicit-map-dot-private.m b/clang/test/Modules/implicit-map-dot-private.m
--- a/clang/test/Modules/implicit-map-dot-private.m
+++ b/clang/test/Modules/implicit-map-dot-private.m
@@ -1,5 +1,17 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -verify -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -F %S/Inputs/implicit-private-canonical -emit-pch -o %t-A.pch %s -Wprivate-module
+
+// Implicit modules.
+// RUN: %clang_cc1 -verify -fmodules -fimplicit-module-maps -fmodules-cache-path=%t \
+// RUN:   -F %S/Inputs/implicit-private-canonical -fsyntax-only %s -Wprivate-module
+
+// Explicit modules.
+// RUN: %clang_cc1 -x objective-c -fmodules -emit-module -fmodule-name=A -o %t/A.pcm \
+// RUN:   %S/Inputs/implicit-private-canonical/A.framework/Modules/module.modulemap -Wprivate-module
+// RUN: %clang_cc1 -x objective-c -fmodules -emit-module -fmodule-name=A_Private -o %t/A_Private.pcm \
+// RUN:   %S/Inputs/implicit-private-canonical/A.framework/Modules/module.private.modulemap -Wprivate-module
+// RUN: %clang_cc1 -verify -fmodules -fimplicit-module-maps -fno-implicit-modules \
+// RUN:   -fmodule-file=A=%t/A.pcm -fmodule-file=A_Private=%t/A_Private.pcm \
+// RUN:   -F %S/Inputs/implicit-private-canonical -fsyntax-only %s -Wprivate-module
 
 #ifndef HEADER
 #define HEADER