diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -2437,11 +2437,12 @@
     }
     if (Writer->Context->getLangOpts().ModulesCodegen) {
       // Under -fmodules-codegen, codegen is performed for all non-internal,
-      // non-always_inline functions.
+      // non-always_inline functions, unless they are available elsewhere.
       if (!FD->hasAttr<AlwaysInlineAttr>()) {
         if (!Linkage)
           Linkage = Writer->Context->GetGVALinkageForFunction(FD);
-        ModulesCodegen = *Linkage != GVA_Internal;
+        ModulesCodegen =
+            *Linkage != GVA_Internal && *Linkage != GVA_AvailableExternally;
       }
     }
   }
diff --git a/clang/test/Modules/codegen-extern-template.h b/clang/test/Modules/codegen-extern-template.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/codegen-extern-template.h
@@ -0,0 +1,12 @@
+// header for codegen-extern-template.cpp
+#ifndef CODEGEN_EXTERN_TEMPLATE_H
+#define CODEGEN_EXTERN_TEMPLATE_H
+
+template <typename T>
+inline T foo() { return 10; }
+
+extern template int foo<int>();
+
+inline int bar() { return foo<int>(); }
+
+#endif
diff --git a/clang/test/Modules/codegen-extern-template.cpp b/clang/test/Modules/codegen-extern-template.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/codegen-extern-template.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fmodules -fmodules-codegen -emit-module -fmodule-name=foo %S/codegen-extern-template.modulemap -x c++ -o %t.pcm
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fmodules -fmodule-file=%t.pcm %s -emit-llvm -o - | FileCheck %s
+// expected-no-diagnostics
+
+#include "codegen-extern-template.h"
+
+template int foo<int>();
+
+// CHECK: define weak_odr i32 @_Z3fooIiET_v
diff --git a/clang/test/Modules/codegen-extern-template.modulemap b/clang/test/Modules/codegen-extern-template.modulemap
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/codegen-extern-template.modulemap
@@ -0,0 +1 @@
+module foo { header "codegen-extern-template.h" }