diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 5456e73956659..882d54f31280a 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2107,8 +2107,8 @@ void ASTDeclMerger::MergeDefinitionData(
     auto *Def = DD.Definition;
     DD = std::move(MergeDD);
     DD.Definition = Def;
-    while ((Def = Def->getPreviousDecl()))
-      cast<CXXRecordDecl>(Def)->DefinitionData = &DD;
+    for (auto *D : Def->redecls())
+      cast<CXXRecordDecl>(D)->DefinitionData = &DD;
     return;
   }
 
diff --git a/clang/test/Modules/GH170084.cpp b/clang/test/Modules/GH170084.cpp
new file mode 100644
index 0000000000000..950499467a6bb
--- /dev/null
+++ b/clang/test/Modules/GH170084.cpp
@@ -0,0 +1,75 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -fmodule-name=stl -fno-cxx-modules -emit-module -fmodules -xc++ stl.cppmap -o stl.pcm
+// RUN: %clang_cc1 -fmodule-name=d -fno-cxx-modules -emit-module -fmodules -fmodule-file=stl.pcm -xc++ d.cppmap -o d.pcm
+// RUN: %clang_cc1 -fmodule-name=b -fno-cxx-modules -emit-module -fmodules -fmodule-file=stl.pcm -xc++ b.cppmap -o b.pcm
+// RUN: %clang_cc1 -fmodule-name=a -fno-cxx-modules -emit-module -fmodules -fmodule-file=stl.pcm -fmodule-file=d.pcm -fmodule-file=b.pcm -xc++ a.cppmap -o a.pcm
+// RUN: %clang_cc1 -fno-cxx-modules -fmodules -fmodule-file=a.pcm -emit-llvm -o /dev/null main.cpp
+
+//--- a.cppmap
+module "a" {
+header "a.h"
+}
+
+//--- a.h
+#include "b.h"
+namespace {
+void a(absl::set<char> c) {
+  absl::set<int> b;
+  c.end();
+  c.contains();
+}
+}  // namespace
+
+//--- b.cppmap
+module "b" {
+header "b.h"
+}
+
+//--- b.h
+#include "c.h"
+void b() { absl::set<char> x; }
+
+//--- c.h
+#include "stl.h"
+namespace absl {
+template <typename>
+class set {
+ public:
+  struct iterator {
+    void u() const;
+  };
+  iterator end() const { return {}; }
+  void contains() const { end().u(); }
+  pair<iterator> e();
+};
+}  // namespace absl
+
+//--- d.cppmap
+module "d" {
+header "d.h"
+}
+
+//--- d.h
+#include "c.h"
+void d() { absl::set<char> x; }
+
+//--- stl.cppmap
+module "stl" {
+header "stl.h"
+}
+
+//--- stl.h
+#ifndef _STL_H_
+#define _STL_H_
+template <class>
+struct pair;
+#endif
+
+//--- main.cpp
+// expected-no-diagnostics
+#include "c.h"
+void f(absl::set<char> o) { o.contains(); }