Index: cfe/trunk/lib/Frontend/CompilerInstance.cpp
===================================================================
--- cfe/trunk/lib/Frontend/CompilerInstance.cpp
+++ cfe/trunk/lib/Frontend/CompilerInstance.cpp
@@ -1601,7 +1601,22 @@
                              Module::NameVisibilityKind Visibility,
                              bool IsInclusionDirective) {
   // Determine what file we're searching from.
-  StringRef ModuleName = Path[0].first->getName();
+  // FIXME: Should we be deciding whether this is a submodule (here and
+  // below) based on -fmodules-ts or should we pass a flag and make the
+  // caller decide?
+  std::string ModuleName;
+  if (getLangOpts().ModulesTS) {
+    // FIXME: Same code as Sema::ActOnModuleDecl() so there is probably a
+    // better place/way to do this.
+    for (auto &Piece : Path) {
+      if (!ModuleName.empty())
+        ModuleName += ".";
+      ModuleName += Piece.first->getName();
+    }
+  }
+  else
+    ModuleName = Path[0].first->getName();
+
   SourceLocation ModuleNameLoc = Path[0].second;
 
   // If we've already handled this import, just return the cached result.
@@ -1816,7 +1831,7 @@
 
   // Verify that the rest of the module path actually corresponds to
   // a submodule.
-  if (Path.size() > 1) {
+  if (!getLangOpts().ModulesTS && Path.size() > 1) {
     for (unsigned I = 1, N = Path.size(); I != N; ++I) {
       StringRef Name = Path[I].first->getName();
       clang::Module *Sub = Module->findSubmodule(Name);
Index: cfe/trunk/test/CXX/modules-ts/dcl.dcl/dcl.module/dcl.module.import/p1.cpp
===================================================================
--- cfe/trunk/test/CXX/modules-ts/dcl.dcl/dcl.module/dcl.module.import/p1.cpp
+++ cfe/trunk/test/CXX/modules-ts/dcl.dcl/dcl.module/dcl.module.import/p1.cpp
@@ -2,13 +2,17 @@
 // RUN: mkdir -p %t
 // RUN: echo 'export module x; export int a, b;' > %t/x.cppm
 // RUN: echo 'export module x.y; export int c;' > %t/x.y.cppm
+// RUN: echo 'export module a.b; export int d;' > %t/a.b.cppm
 //
 // RUN: %clang_cc1 -std=c++1z -fmodules-ts -emit-module-interface %t/x.cppm -o %t/x.pcm
 // RUN: %clang_cc1 -std=c++1z -fmodules-ts -emit-module-interface -fmodule-file=%t/x.pcm %t/x.y.cppm -o %t/x.y.pcm
+// RUN: %clang_cc1 -std=c++1z -fmodules-ts -emit-module-interface %t/a.b.cppm -o %t/a.b.pcm
 //
-// RUN: %clang_cc1 -std=c++1z -fmodules-ts -I%t -fmodule-file=%t/x.y.pcm -verify %s \
+// RUN: %clang_cc1 -std=c++1z -fmodules-ts -I%t -fmodule-file=%t/x.y.pcm -fmodule-file=%t/a.b.pcm -verify %s \
 // RUN:            -DMODULE_NAME=z
-// RUN: %clang_cc1 -std=c++1z -fmodules-ts -I%t -fmodule-file=%t/x.y.pcm -verify %s \
+// RUN: %clang_cc1 -std=c++1z -fmodules-ts -I%t -fmodule-file=%t/x.y.pcm -fmodule-file=%t/a.b.pcm -verify %s \
+// RUN:            -DMODULE_NAME=a.b
+// RUN: %clang_cc1 -std=c++1z -fmodules-ts -I%t -fmodule-file=%t/x.y.pcm -fmodule-file=%t/a.b.pcm -verify %s \
 // RUN:            -DMODULE_X -DMODULE_NAME=x
 
 module MODULE_NAME;
@@ -33,6 +37,7 @@
 import x [[blarg::noreturn]]; // expected-warning {{unknown attribute 'noreturn' ignored}}
 
 import x.y;
+import a.b; // Does not imply existence of module a.
 import x.; // expected-error {{expected a module name after 'import'}}
 import .x; // expected-error {{expected a module name after 'import'}}