Index: clang/include/clang/Basic/Module.h
===================================================================
--- clang/include/clang/Basic/Module.h
+++ clang/include/clang/Basic/Module.h
@@ -524,6 +524,11 @@
            Kind == ModulePartitionImplementation;
   }
 
+  // Is this a C++20 module interface or a partition.
+  bool isInterfaceOrPartition() const {
+    return Kind == ModuleInterfaceUnit || isModulePartition();
+  }
+
   /// Get the primary module interface name from a partition.
   StringRef getPrimaryModuleInterfaceName() const {
     if (isModulePartition()) {
Index: clang/lib/Serialization/ASTWriterDecl.cpp
===================================================================
--- clang/lib/Serialization/ASTWriterDecl.cpp
+++ clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1022,12 +1022,12 @@
     if (Writer.WritingModule &&
         !D->getDescribedVarTemplate() && !D->getMemberSpecializationInfo() &&
         !isa<VarTemplateSpecializationDecl>(D)) {
-      // When building a C++ Modules TS module interface unit, a strong
-      // definition in the module interface is provided by the compilation of
-      // that module interface unit, not by its users. (Inline variables are
-      // still emitted in module users.)
+      // When building a C++20 module interface unit or a partition unit, a
+      // strong definition in the module interface is provided by the
+      // compilation of that unit, not by its users. (Inline variables are still
+      // emitted in module users.)
       ModulesCodegen =
-          (Writer.WritingModule->Kind == Module::ModuleInterfaceUnit ||
+          (Writer.WritingModule->isInterfaceOrPartition() ||
            (D->hasAttr<DLLExportAttr>() &&
             Writer.Context->getLangOpts().BuildingPCHWithObjectFile)) &&
           Writer.Context->GetGVALinkageForVariable(D) == GVA_StrongExternal;
@@ -2463,11 +2463,11 @@
   if (!FD->isDependentContext()) {
     Optional<GVALinkage> Linkage;
     if (Writer->WritingModule &&
-        Writer->WritingModule->Kind == Module::ModuleInterfaceUnit) {
-      // When building a C++ Modules TS module interface unit, a strong
-      // definition in the module interface is provided by the compilation of
-      // that module interface unit, not by its users. (Inline functions are
-      // still emitted in module users.)
+        Writer->WritingModule->isInterfaceOrPartition()) {
+      // When building a C++20 module interface unit or a partition unit, a
+      // strong definition in the module interface is provided by the
+      // compilation of that unit, not by its users. (Inline functions are still
+      // emitted in module users.)
       Linkage = Writer->Context->GetGVALinkageForFunction(FD);
       ModulesCodegen = *Linkage == GVA_StrongExternal;
     }
Index: clang/test/CodeGenCXX/partitions.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/partitions.cpp
@@ -0,0 +1,50 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/parta.cppm -o %t/mod-parta.pcm
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/partb.cppm -o %t/mod-partb.pcm
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface -fmodule-file=%t/mod-parta.pcm \
+// RUN:     -fmodule-file=%t/mod-partb.pcm %t/mod.cppm -o %t/mod.pcm
+// RUN: %clang_cc1 -std=c++20 %t/mod.pcm -S -emit-llvm -disable-llvm-passes -o - \
+// RUN:     | FileCheck %t/mod.cppm
+// RUN: %clang_cc1 -std=c++20 -O2 -emit-module-interface -fmodule-file=%t/mod-parta.pcm \
+// RUN:     -fmodule-file=%t/mod-partb.pcm %t/mod.cppm -o %t/mod.pcm
+// RUN: %clang_cc1 -std=c++20 -O2 %t/mod.pcm -S -emit-llvm -disable-llvm-passes -o - \
+// RUN:     | FileCheck %t/mod.cppm  -check-prefix=CHECK-OPT
+
+//--- parta.cppm
+export module mod:parta;
+
+export int a = 43;
+
+export int foo() {
+  return 3 + a;
+}
+
+//--- partb.cppm
+export module mod:partb;
+
+export int b = 43;
+
+export int bar() {
+  return 43 + b;
+}
+
+//--- mod.cppm
+export module mod;
+import :parta;
+import :partb;
+export int use() {
+  return foo() + bar() + a + b;
+}
+
+// CHECK: @a = available_externally global
+// CHECK: @b = available_externally global
+// CHECK: declare noundef i32 @_Z3foov
+// CHECK: declare noundef i32 @_Z3barv
+
+// CHECK-OPT: @a = available_externally global
+// CHECK-OPT: @b = available_externally global
+// CHECK-OPT: define available_externally noundef i32 @_Z3foov
+// CHECK-OPT: define available_externally noundef i32 @_Z3barv