diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -192,10 +192,11 @@
 
   const ModuleMap &MM = HS.getModuleMap();
 
-  auto ProcessModuleOnce = [&](const Module *Mod) {
-    if (ProcessedModules.insert(Mod).second)
-      if (auto ModuleMapFile = MM.getModuleMapFileForUniquing(Mod))
-        ModuleMaps.insert(*ModuleMapFile);
+  auto ProcessModuleOnce = [&](const Module *M) {
+    for (const Module *Mod = M; Mod; Mod = Mod->Parent)
+      if (ProcessedModules.insert(Mod).second)
+        if (auto ModuleMapFile = MM.getModuleMapFileForUniquing(Mod))
+          ModuleMaps.insert(*ModuleMapFile);
   };
 
   for (const Module *CurrentModule : ModulesToProcess) {
diff --git a/clang/test/ClangScanDeps/modules-extern-submodule.c b/clang/test/ClangScanDeps/modules-extern-submodule.c
new file mode 100644
--- /dev/null
+++ b/clang/test/ClangScanDeps/modules-extern-submodule.c
@@ -0,0 +1,128 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+//--- tu.m
+@import first;
+
+//--- first/first/module.modulemap
+module first { header "first.h" }
+//--- first/first/first.h
+#include <second/sub.h>
+
+//--- second/second/module.modulemap
+module second { extern module sub "sub.modulemap" }
+//--- second/second/sub.modulemap
+module second.sub { header "sub.h" }
+//--- second/second/sub.h
+@import third;
+
+//--- third/module.modulemap
+module third {}
+
+//--- cdb.json.template
+[{
+  "file": "DIR/tu.c",
+  "directory": "DIR",
+  "command": "clang -I DIR/first -I DIR/second -I DIR/third -fmodules -fmodules-cache-path=DIR/cache -c DIR/tu.m -o DIR/tu.o"
+}]
+
+// RUN: sed "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full > %t/result.json
+// RUN: cat %t/result.json | sed 's:\\\\\?:/:g' | FileCheck %s -DPREFIX=%/t
+
+// CHECK:       {
+// CHECK-NEXT:   "modules": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "context-hash": "{{.*}}",
+// CHECK-NEXT:           "module-name": "second"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/first/first/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK-NEXT:         "-cc1",
+// CHECK:              "-fmodule-map-file=[[PREFIX]]/second/second/module.modulemap"
+// CHECK-NOT:          "-fmodule-map-file=[[PREFIX]]/second/second/sub.modulemap"
+// CHECK-NOT:          "-fmodule-map-file=[[PREFIX]]/third/module.modulemap"
+// CHECK:              "-fmodule-file=second=[[PREFIX]]/cache/{{.*}}/second-{{.*}}.pcm"
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/first/first/first.h",
+// CHECK-NEXT:         "[[PREFIX]]/first/first/module.modulemap",
+// CHECK-NEXT:         "[[PREFIX]]/second/second/module.modulemap",
+// CHECK-NEXT:         "[[PREFIX]]/second/second/sub.modulemap"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "first"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "context-hash": "{{.*}}",
+// CHECK-NEXT:           "module-name": "third"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/second/second/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK-NEXT:         "-cc1",
+// CHECK:              "-fmodule-map-file=[[PREFIX]]/third/module.modulemap",
+// CHECK:              "-fmodule-file=third=[[PREFIX]]/cache/{{.*}}/third-{{.*}}.pcm",
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/second/second/module.modulemap",
+// CHECK-NEXT:         "[[PREFIX]]/second/second/sub.h",
+// CHECK-NEXT:         "[[PREFIX]]/second/second/sub.modulemap",
+// CHECK-NEXT:         "[[PREFIX]]/third/module.modulemap"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "second"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps": [],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/third/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK-NEXT:         "-cc1",
+// CHECK-NOT:          "-fmodule-map-file=
+// CHECK-NOT:          "-fmodule-file=third=
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/third/module.modulemap"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "third"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ],
+// CHECK-NEXT:   "translation-units": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "commands": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "clang-context-hash": "{{.*}}",
+// CHECK-NEXT:           "clang-module-deps": [
+// CHECK-NEXT:             {
+// CHECK-NEXT:               "context-hash": "{{.*}}",
+// CHECK-NEXT:               "module-name": "first"
+// CHECK-NEXT:             }
+// CHECK-NEXT:           ],
+// CHECK-NEXT:           "command-line": [
+// CHECK-NEXT:             "-cc1",
+// CHECK:                  "-fmodule-map-file=[[PREFIX]]/first/first/module.modulemap",
+// CHECK:                  "-fmodule-file=first=[[PREFIX]]/cache/{{.*}}/first-{{.*}}.pcm",
+// CHECK:                ],
+// CHECK-NEXT:           "executable": "clang",
+// CHECK-NEXT:           "file-deps": [
+// CHECK-NEXT:             "[[PREFIX]]/tu.m"
+// CHECK-NEXT:           ],
+// CHECK-NEXT:           "input-file": "[[PREFIX]]/tu.c"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ]
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ]
+// CHECK-NEXT: }
+
+// RUN: %deps-to-rsp %t/result.json --module-name=third > %t/third.cc1.rsp
+// RUN: %deps-to-rsp %t/result.json --module-name=second > %t/second.cc1.rsp
+// RUN: %deps-to-rsp %t/result.json --module-name=first > %t/first.cc1.rsp
+// RUN: %clang @%t/third.cc1.rsp
+// RUN: %clang @%t/second.cc1.rsp
+// RUN: %clang @%t/first.cc1.rsp