Index: include/clang/Basic/DiagnosticLexKinds.td
===================================================================
--- include/clang/Basic/DiagnosticLexKinds.td
+++ include/clang/Basic/DiagnosticLexKinds.td
@@ -594,8 +594,6 @@
 def err_mmap_module_redefinition : Error<
   "redefinition of module '%0'">;
 def note_mmap_prev_definition : Note<"previously defined here">;
-def err_mmap_umbrella_dir_not_found : Error<
-  "umbrella directory '%0' not found">;
 def err_mmap_umbrella_clash : Error<
   "umbrella for module '%0' already covers this directory">;
 def err_mmap_module_id : Error<
@@ -656,6 +654,9 @@
 def warn_uncovered_module_header : Warning<
   "umbrella header for module '%0' does not include header '%1'">, 
   InGroup<IncompleteUmbrella>;
+def warn_mmap_umbrella_dir_not_found : Warning<
+  "umbrella directory '%0' not found">,
+  InGroup<IncompleteUmbrella>;
 def err_expected_id_building_module : Error<
   "expected a module name in '__building_module' expression">;
 def warn_use_of_private_header_outside_module : Warning<
Index: lib/Lex/ModuleMap.cpp
===================================================================
--- lib/Lex/ModuleMap.cpp
+++ lib/Lex/ModuleMap.cpp
@@ -2002,9 +2002,8 @@
   }
   
   if (!Dir) {
-    Diags.Report(DirNameLoc, diag::err_mmap_umbrella_dir_not_found)
+    Diags.Report(DirNameLoc, diag::warn_mmap_umbrella_dir_not_found)
       << DirName;
-    HadError = true;
     return;
   }
 
Index: test/Modules/umbrella-header-include-builtin.mm
===================================================================
--- test/Modules/umbrella-header-include-builtin.mm
+++ test/Modules/umbrella-header-include-builtin.mm
@@ -4,3 +4,11 @@
 // RUN: %clang -cc1 -fsyntax-only -nostdinc++ -isysroot %S/Inputs/libc-libcxx/sysroot -isystem %S/Inputs/libc-libcxx/sysroot/usr/include/c++/v1 -F%S/Inputs/libc-libcxx/sysroot/Frameworks -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x objective-c++ %s
 
 #include <A/A.h>
+
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: echo "module NonExistent1 { umbrella \"NonExistent\" }" > %t/modules.modulemap
+// RUN: echo "" > %t/A.h
+// RUN: echo "#include \"A.h\"  int i;" > %t/T.cxx
+// RUN: %clang -I %t -fmodules -fsyntax-only %t/T.cxx
+// expected-warning {{ umbrella directory }}