diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1625,22 +1625,20 @@
   Module *NewM = New->getOwningModule();
   Module *OldM = Old->getOwningModule();
 
-  if (NewM && NewM->Kind == Module::PrivateModuleFragment)
+  if (NewM && NewM->isPrivateModule())
     NewM = NewM->Parent;
-  if (OldM && OldM->Kind == Module::PrivateModuleFragment)
+  if (OldM && OldM->isPrivateModule())
     OldM = OldM->Parent;
 
-  // If we have a decl in a module partition, it is part of the containing
-  // module (which is the only thing that can be importing it).
-  if (NewM && OldM &&
-      (OldM->Kind == Module::ModulePartitionInterface ||
-       OldM->Kind == Module::ModulePartitionImplementation)) {
-    return false;
-  }
-
   if (NewM == OldM)
     return false;
 
+  // Partitions are part of the module, but a partition could import another
+  // module, so verify that the PMIs agree.
+  if (NewM && OldM && (NewM->isModulePartition() || OldM->isModulePartition()))
+    return NewM->getPrimaryModuleInterfaceName() ==
+           OldM->getPrimaryModuleInterfaceName();
+
   bool NewIsModuleInterface = NewM && NewM->isModulePurview();
   bool OldIsModuleInterface = OldM && OldM->isModulePurview();
   if (NewIsModuleInterface || OldIsModuleInterface) {
diff --git a/clang/test/Modules/cxx20-partition-redeclarations.cpp b/clang/test/Modules/cxx20-partition-redeclarations.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/cxx20-partition-redeclarations.cpp
@@ -0,0 +1,55 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -std=c++20 A-intf-part.cpp -emit-module-interface \
+// RUN:  -o A-PubPart.pcm
+// RUN: %clang_cc1 -std=c++20 A-interface.cpp -emit-module-interface \
+// RUN:   -fmodule-file=A-PubPart.pcm -o A.pcm
+
+// RUN: %clang_cc1 -std=c++20 A-impl-top.cpp -fsyntax-only -fmodule-file=A.pcm
+// RUN: %clang_cc1 -std=c++20 A-impl-part.cpp -fsyntax-only -fmodule-file=A.pcm
+// RUN: %clang_cc1 -std=c++20 A-impl-1.cpp -fsyntax-only -fmodule-file=A.pcm
+// RUN: %clang_cc1 -std=c++20 A-impl-2.cpp -fsyntax-only -fmodule-file=A.pcm
+
+//--- A-interface.cpp
+export module A;
+
+export import :PubPart;
+
+export void do_something();
+
+void helper1();
+void helper3();
+
+//--- A-intf-part.cpp
+export module A:PubPart;
+
+void helper2();
+
+//--- A-impl-top.cpp
+
+module A;
+
+void do_something() {
+  helper1();
+  helper2();
+  helper3();
+}
+
+//--- A-impl-part.cpp
+module A:Secret;
+
+import A;
+
+void helper3() {}
+
+//--- A-impl-1.cpp
+module A;
+
+void helper1() {}
+
+//--- A-impl-2.cpp
+module A;
+
+void helper2() {}