diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -888,6 +888,8 @@
   InGroup<DiagGroup<"private-header">>, DefaultError;
 def err_undeclared_use_of_module : Error<
   "module %0 does not depend on a module exporting '%1'">;
+def err_undeclared_use_of_module_indirect : Error<
+  "module %0 does not directly depend on a module exporting '%1', which is part of indirectly-used module %2">;
 def warn_non_modular_include_in_framework_module : Warning<
   "include of non-modular header inside framework module '%0': '%1'">,
   InGroup<NonModularIncludeInFrameworkModule>, DefaultIgnore;
diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -528,8 +528,9 @@
 
   // We have found a module, but we don't use it.
   if (NotUsed) {
-    Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module)
-        << RequestingModule->getTopLevelModule()->Name << Filename;
+    Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module_indirect)
+        << RequestingModule->getTopLevelModule()->Name << Filename
+        << NotUsed->Name;
     return;
   }
 
diff --git a/clang/test/Modules/Inputs/declare-use/h.h b/clang/test/Modules/Inputs/declare-use/h.h
--- a/clang/test/Modules/Inputs/declare-use/h.h
+++ b/clang/test/Modules/Inputs/declare-use/h.h
@@ -1,7 +1,7 @@
 #ifndef H_H
 #define H_H
 #include "c.h"
-#include "d.h" // expected-error {{module XH does not depend on a module exporting}}
+#include "d.h" // expected-error {{module XH does not directly depend on a module exporting 'd.h', which is part of indirectly-used module XD}}
 #include "h1.h"
 const int h1 = aux_h*c*7*d;
 #endif
diff --git a/clang/test/Modules/declare-use-textual.cpp b/clang/test/Modules/declare-use-textual.cpp
--- a/clang/test/Modules/declare-use-textual.cpp
+++ b/clang/test/Modules/declare-use-textual.cpp
@@ -2,5 +2,5 @@
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=Textual -I %S/Inputs/declare-use %s -verify
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=Textual -I %S/Inputs/declare-use %s -fno-modules-validate-textual-header-includes
 
-// expected-error@textual.h:* {{module Textual does not depend on a module exporting 'a.h'}}
+// expected-error@textual.h:* {{module Textual does not directly depend on a module exporting 'a.h', which is part of indirectly-used module XA}}
 #include "textual.h"
diff --git a/clang/test/Modules/declare-use1.cpp b/clang/test/Modules/declare-use1.cpp
--- a/clang/test/Modules/declare-use1.cpp
+++ b/clang/test/Modules/declare-use1.cpp
@@ -6,7 +6,7 @@
 
 #include "g.h"
 #include "e.h"
-#include "f.h" // expected-error {{module XG does not depend on a module exporting 'f.h'}}
+#include "f.h" // expected-error {{module XG does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 #include "i.h"
 #include "sub.h"
 const int g2 = g1 + e + f + aux_i + sub;
diff --git a/clang/test/Modules/declare-use2.cpp b/clang/test/Modules/declare-use2.cpp
--- a/clang/test/Modules/declare-use2.cpp
+++ b/clang/test/Modules/declare-use2.cpp
@@ -3,5 +3,5 @@
 
 #include "h.h"
 #include "e.h"
-#include "f.h" // expected-error {{module XH does not depend on a module exporting 'f.h'}}
+#include "f.h" // expected-error {{module XH does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 const int h2 = h1+e+f;
diff --git a/clang/test/Modules/declare-use3.cpp b/clang/test/Modules/declare-use3.cpp
--- a/clang/test/Modules/declare-use3.cpp
+++ b/clang/test/Modules/declare-use3.cpp
@@ -1,4 +1,4 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -include "g.h" -include "e.h" -include "f.h" -include "i.h" -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=XG -I %S/Inputs/declare-use %s -verify
-// expected-error {{module XG does not depend on a module exporting 'f.h'}}
+// expected-error {{module XG does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 const int g2 = g1 + e + f + aux_i;
diff --git a/clang/test/Modules/strict-decluse.cpp b/clang/test/Modules/strict-decluse.cpp
--- a/clang/test/Modules/strict-decluse.cpp
+++ b/clang/test/Modules/strict-decluse.cpp
@@ -3,7 +3,7 @@
 
 #include "g.h"
 #include "e.h"
-#include "f.h" // expected-error {{module XG does not depend on a module exporting 'f.h'}}
+#include "f.h" // expected-error {{module XG does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 #include "i.h" // expected-error {{module XG does not depend on a module exporting 'i.h'}}
 
 const int g2 = g1 + e + f + aux_i;
diff --git a/clang/test/Modules/string_names.cpp b/clang/test/Modules/string_names.cpp
--- a/clang/test/Modules/string_names.cpp
+++ b/clang/test/Modules/string_names.cpp
@@ -6,5 +6,5 @@
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-decluse -I %S/Inputs/string_names %t/test.ii -fmodule-name="my/module-a"
 
 #include "a.h"
-#include "b.h" // expected-error {{does not depend on a module exporting}}
+#include "b.h" // expected-error {{module my/module-a does not directly depend on a module exporting 'b.h', which is part of indirectly-used module my/module-b}}
 #include "c.h"
diff --git a/clang/test/Modules/textual-headers.cpp b/clang/test/Modules/textual-headers.cpp
--- a/clang/test/Modules/textual-headers.cpp
+++ b/clang/test/Modules/textual-headers.cpp
@@ -6,9 +6,9 @@
 #include "k.h"
 
 #define GIMME_AN_L
-#include "l.h" // expected-error {{module XG does not depend on a module exporting 'l.h'}}
+#include "l.h" // expected-error {{module XG does not directly depend on a module exporting 'l.h', which is part of indirectly-used module XL}}
 
-#include "m2.h" // expected-error {{module XG does not depend on a module exporting 'm2.h'}}
+#include "m2.h" // expected-error {{module XG does not directly depend on a module exporting 'm2.h', which is part of indirectly-used module XM}}
 const int use_m = m; // expected-error {{undeclared identifier}}
 
 #define GIMME_AN_M