diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -417,7 +417,8 @@
 
   IsInHeaderMap = true;
 
-  auto FixupSearchPath = [&]() {
+  auto FixupSearchPathAndFindUsableModule =
+      [&](auto file) -> Optional<FileEntryRef> {
     if (SearchPath) {
       StringRef SearchPathRef(getName());
       SearchPath->clear();
@@ -427,6 +428,12 @@
       RelativePath->clear();
       RelativePath->append(Filename.begin(), Filename.end());
     }
+    if (!HS.findUsableModuleForHeader(
+            &file.getFileEntry(), file.getFileEntry().getDir(),
+            RequestingModule, SuggestedModule, isSystemHeaderDirectory())) {
+      return None;
+    }
+    return file;
   };
 
   // Check if the headermap maps the filename to a framework include
@@ -437,12 +444,10 @@
     Filename = StringRef(MappedName.begin(), MappedName.size());
     Optional<FileEntryRef> Result = HM->LookupFile(Filename, HS.getFileMgr());
     if (Result) {
-      FixupSearchPath();
-      return *Result;
+      return FixupSearchPathAndFindUsableModule(*Result);
     }
   } else if (auto Res = HS.getFileMgr().getOptionalFileRef(Dest)) {
-    FixupSearchPath();
-    return *Res;
+    return FixupSearchPathAndFindUsableModule(*Res);
   }
 
   return None;
diff --git a/clang/test/Modules/Inputs/implicit-module-header-maps/a.h b/clang/test/Modules/Inputs/implicit-module-header-maps/a.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/implicit-module-header-maps/a.h
@@ -0,0 +1,3 @@
+#ifdef FOO
+#error foo
+#endif
diff --git a/clang/test/Modules/Inputs/implicit-module-header-maps/a.hmap.json b/clang/test/Modules/Inputs/implicit-module-header-maps/a.hmap.json
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/implicit-module-header-maps/a.hmap.json
@@ -0,0 +1,7 @@
+{
+  "mappings" :
+    {
+     "Before/Mapping.h" : "After/Mapping.h",
+     "After/Mapping.h" : "After/Mapping.h"
+    }
+}
diff --git a/clang/test/Modules/Inputs/implicit-module-header-maps/a.module.modulemap b/clang/test/Modules/Inputs/implicit-module-header-maps/a.module.modulemap
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/implicit-module-header-maps/a.module.modulemap
@@ -0,0 +1,3 @@
+module a {
+  header "After/Mapping.h"
+}
diff --git a/clang/test/Modules/Inputs/implicit-module-header-maps/b.hmap.json b/clang/test/Modules/Inputs/implicit-module-header-maps/b.hmap.json
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/Inputs/implicit-module-header-maps/b.hmap.json
@@ -0,0 +1,6 @@
+{
+  "mappings" :
+    {
+     "Before/Mapping.h" : "OUTPUTS_DIR/After/Mapping.h"
+    }
+}
diff --git a/clang/test/Modules/implicit-module-header-maps.cpp b/clang/test/Modules/implicit-module-header-maps.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/implicit-module-header-maps.cpp
@@ -0,0 +1,29 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: cd %t
+//
+// RUN: %hmaptool write %S/Inputs/implicit-module-header-maps/a.hmap.json %t/hmap
+//
+// RUN: mkdir -p %t/After
+// RUN: cp %S/Inputs/implicit-module-header-maps/a.h %t/After/Mapping.h
+// RUN: cp %S/Inputs/implicit-module-header-maps/a.module.modulemap %t/module.modulemap
+//
+// RUN: %clang -Rmodule-build -fmodules -fimplicit-modules -fimplicit-module-maps -fmodule-map-file=%t/module.modulemap -fsyntax-only %s -I %t/hmap
+//
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: cd %t
+//
+// RUN: sed -e "s|OUTPUTS_DIR|%t|g" %S/Inputs/implicit-module-header-maps/b.hmap.json > %t/hmap.json
+// RUN: %hmaptool write %t/hmap.json %t/hmap
+//
+// RUN: mkdir -p %t/After
+// RUN: cp %S/Inputs/implicit-module-header-maps/a.h %t/After/Mapping.h
+// RUN: cp %S/Inputs/implicit-module-header-maps/a.module.modulemap %t/module.modulemap
+//
+// RUN: %clang -Rmodule-build -fmodules -fimplicit-modules -fimplicit-module-maps -fmodule-map-file=%t/module.modulemap -fsyntax-only %s -I %t/hmap
+
+#define FOO
+// This include will fail if modules weren't used.  The include name itself
+// doesn't exist and relies on the header map to remap it to the real header.
+#include "Before/Mapping.h"