Index: include/clang/Lex/HeaderSearch.h
===================================================================
--- include/clang/Lex/HeaderSearch.h
+++ include/clang/Lex/HeaderSearch.h
@@ -503,8 +503,12 @@
   /// search directories to produce a module definition. If not, this lookup
   /// will only return an already-known module.
   ///
+  /// \param SearchTopLevelOnly Whether we are allowed to search the
+  /// subdirectories to produce a module definition.
+  ///
   /// \returns The module with the given name.
-  Module *lookupModule(StringRef ModuleName, bool AllowSearch = true);
+  Module *lookupModule(StringRef ModuleName, bool AllowSearch = true,
+                       bool SearchTopLevelOnly = false);
 
   /// \brief Try to find a module map file in the given directory, returning
   /// \c nullptr if none is found.
@@ -560,7 +564,6 @@
   void loadTopLevelSystemModules();
 
 private:
-
   /// \brief Lookup a module with the given module name and search-name.
   ///
   /// \param ModuleName The name of the module we're looking for.
@@ -570,8 +573,12 @@
   /// but for compatibility with some buggy frameworks, additional attempts
   /// may be made to find the module under a related-but-different search-name.
   ///
+  /// \param SearchTopLevelOnly Whether we are allowed to search the
+  /// subdirectories to produce a module definition.
+  ///
   /// \returns The module named ModuleName.
-  Module *lookupModule(StringRef ModuleName, StringRef SearchName);
+  Module *lookupModule(StringRef ModuleName, StringRef SearchName,
+                       bool SearchTopLevelOnly);
 
   /// \brief Retrieve a module with the given name, which may be part of the
   /// given framework.
Index: lib/Lex/HeaderSearch.cpp
===================================================================
--- lib/Lex/HeaderSearch.cpp
+++ lib/Lex/HeaderSearch.cpp
@@ -191,14 +191,15 @@
   return Result.str().str();
 }
 
-Module *HeaderSearch::lookupModule(StringRef ModuleName, bool AllowSearch) {
+Module *HeaderSearch::lookupModule(StringRef ModuleName, bool AllowSearch,
+                                   bool SearchTopLevelOnly) {
   // Look in the module map to determine if there is a module by this name.
   Module *Module = ModMap.findModule(ModuleName);
   if (Module || !AllowSearch || !HSOpts->ImplicitModuleMaps)
     return Module;
 
   StringRef SearchName = ModuleName;
-  Module = lookupModule(ModuleName, SearchName);
+  Module = lookupModule(ModuleName, SearchName, SearchTopLevelOnly);
 
   // The facility for "private modules" -- adjacent, optional module maps named
   // module.private.modulemap that are supposed to define private submodules --
@@ -208,11 +209,12 @@
   // Foo.framework, when we previously looked and failed to find a
   // FooPrivate.framework.
   if (!Module && SearchName.consume_back("Private"))
-    Module = lookupModule(ModuleName, SearchName);
+    Module = lookupModule(ModuleName, SearchName, SearchTopLevelOnly);
   return Module;
 }
 
-Module *HeaderSearch::lookupModule(StringRef ModuleName, StringRef SearchName) {
+Module *HeaderSearch::lookupModule(StringRef ModuleName, StringRef SearchName,
+                                   bool SearchTopLevelOnly) {
   Module *Module = nullptr;
 
   // Look through the various header search paths to load any available module
@@ -267,7 +269,7 @@
 
     // If we've already performed the exhaustive search for module maps in this
     // search directory, don't do it again.
-    if (SearchDirs[Idx].haveSearchedAllModuleMaps())
+    if (SearchTopLevelOnly || SearchDirs[Idx].haveSearchedAllModuleMaps())
       continue;
 
     // Load all module maps in the immediate subdirectories of this search
Index: lib/Serialization/ASTReader.cpp
===================================================================
--- lib/Serialization/ASTReader.cpp
+++ lib/Serialization/ASTReader.cpp
@@ -2551,7 +2551,9 @@
              "MODULE_DIRECTORY found before MODULE_NAME");
       // If we've already loaded a module map file covering this module, we may
       // have a better path for it (relative to the current build).
-      Module *M = PP.getHeaderSearchInfo().lookupModule(F.ModuleName);
+      Module *M = PP.getHeaderSearchInfo().lookupModule(
+          F.ModuleName,
+          /*AllowSearch*/ true, /*SearchTopLevelOnly*/ true);
       if (M && M->Directory) {
         // If we're implicitly loading a module, the base directory can't
         // change between the build and use.
Index: test/Modules/Inputs/PR31905/my-project/module.modulemap
===================================================================
--- /dev/null
+++ test/Modules/Inputs/PR31905/my-project/module.modulemap
@@ -0,0 +1,3 @@
+module my_project {
+  header "my-header.h"
+}
Index: test/Modules/Inputs/PR31905/my-project/my-header.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/PR31905/my-project/my-header.h
@@ -0,0 +1,4 @@
+#ifndef MY_HEADER_H
+#define MY_HEADER_H
+#include <stddef.h>
+#endif
Index: test/Modules/pr31905.cpp
===================================================================
--- /dev/null
+++ test/Modules/pr31905.cpp
@@ -0,0 +1,9 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: cp -R %S/Inputs/PR31905 %t/other-include
+// RUN: %clang_cc1 -std=c++11 -I%S/Inputs/PR31905/ -I%t/other-include -fmodules -fmodules-local-submodule-visibility \
+// RUN:    -fimplicit-module-maps -fmodules-cache-path=%t -verify %s
+
+#include "my-project/my-header.h"
+
+int main() {} // expected-no-diagnostics