diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 93eecbe0e1363..01c4ee97662b6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1049,6 +1049,11 @@ Bug Fixes to C++ Support
 
 - Set the ``__cpp_auto_cast`` feature test macro in C++23 mode.
 
+- Fix crash for inconsistent deducing state of function return types
+  in importing modules.
+  Fixes (`#78830 <https://github.com/llvm/llvm-project/issues/78830>`_)
+  Fixes (`#60085 <https://github.com/llvm/llvm-project/issues/60085>`_)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index 21d791f5cd89a..dd1451bbf2d2c 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -550,6 +550,10 @@ class ASTReader
   /// declaration and the value is the deduced return type.
   llvm::SmallMapVector<FunctionDecl *, QualType, 4> PendingDeducedTypeUpdates;
 
+  /// Functions has undededuced return type and we wish we can find the deduced
+  /// return type by iterating the redecls in other modules.
+  llvm::SmallVector<FunctionDecl *, 4> PendingUndeducedFunctionDecls;
+
   /// Declarations that have been imported and have typedef names for
   /// linkage purposes.
   llvm::DenseMap<std::pair<DeclContext *, IdentifierInfo *>, NamedDecl *>
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index fe8782a3eb9e7..fecd94e875f67 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -9534,12 +9534,21 @@ void ASTReader::finishPendingActions() {
       auto *FD = PendingDeducedFunctionTypes[I].first;
       FD->setType(GetType(PendingDeducedFunctionTypes[I].second));
 
-      // If we gave a function a deduced return type, remember that we need to
-      // propagate that along the redeclaration chain.
-      auto *DT = FD->getReturnType()->getContainedDeducedType();
-      if (DT && DT->isDeduced())
-        PendingDeducedTypeUpdates.insert(
-            {FD->getCanonicalDecl(), FD->getReturnType()});
+      if (auto *DT = FD->getReturnType()->getContainedDeducedType()) {
+        // If we gave a function a deduced return type, remember that we need to
+        // propagate that along the redeclaration chain.
+        if (DT->isDeduced()) {
+          PendingDeducedTypeUpdates.insert(
+              {FD->getCanonicalDecl(), FD->getReturnType()});
+          continue;
+        }
+
+        // The function has undeduced DeduceType return type. We hope we can
+        // find the deduced type by iterating the redecls in other modules
+        // later.
+        PendingUndeducedFunctionDecls.push_back(FD);
+        continue;
+      }
     }
     PendingDeducedFunctionTypes.clear();
 
@@ -10105,6 +10114,13 @@ void ASTReader::FinishedDeserializing() {
         getContext().adjustDeducedFunctionResultType(Update.first,
                                                      Update.second);
       }
+
+      auto UDTUpdates = std::move(PendingUndeducedFunctionDecls);
+      PendingUndeducedFunctionDecls.clear();
+      // We hope we can find the deduced type for the functions by iterating
+      // redeclarations in other modules.
+      for (FunctionDecl *UndeducedFD : UDTUpdates)
+        (void)UndeducedFD->getMostRecentDecl();
     }
 
     if (ReadTimer)
diff --git a/clang/test/Modules/pr60085.cppm b/clang/test/Modules/pr60085.cppm
new file mode 100644
index 0000000000000..fd6fd914a543c
--- /dev/null
+++ b/clang/test/Modules/pr60085.cppm
@@ -0,0 +1,85 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/d.cppm \
+// RUN:     -emit-module-interface -o %t/d.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/c.cppm \
+// RUN:     -emit-module-interface -o %t/c.pcm -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/b.cppm \
+// RUN:     -emit-module-interface -o %t/b.pcm -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/a.cppm \
+// RUN:     -emit-module-interface -o %t/a.pcm -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/a.pcm \
+// RUN:     -S -emit-llvm -disable-llvm-passes -o - -fprebuilt-module-path=%t \
+// RUN:     | FileCheck %t/a.cppm
+
+//--- d.cppm
+export module d;
+
+export template<typename>
+struct integer {
+	using type = int;
+
+	static constexpr auto value() {
+		return 0;
+	}
+
+	friend constexpr void f(integer const x) {
+		x.value();
+	}
+};
+
+export constexpr void ddd(auto const value) {
+	f(value);
+}
+
+
+template<typename T>
+constexpr auto dd = T();
+
+export template<typename T>
+constexpr auto d() {
+	dd<T>;
+}
+
+//--- c.cppm
+export module c;
+
+import d;
+
+template<typename T>
+auto cc = T();
+
+auto c() {
+	cc<integer<int>>;
+	integer<int>().value();
+}
+
+//--- b.cppm
+export module b;
+
+import d;
+
+auto b() {
+	integer<int>::type;
+}
+
+//--- a.cppm
+export module a;
+
+import b;
+import c;
+import d;
+
+constexpr void aa() {
+	d<integer<unsigned>>();
+	ddd(integer<int>());
+}
+
+export extern "C" void a() {
+	aa();
+}
+
+// Checks that we emit the IR successfully.
+// CHECK: define{{.*}}@a(
diff --git a/clang/test/Modules/pr78830.cppm b/clang/test/Modules/pr78830.cppm
new file mode 100644
index 0000000000000..a3b1a8021ebea
--- /dev/null
+++ b/clang/test/Modules/pr78830.cppm
@@ -0,0 +1,56 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/Type.cppm -emit-module-interface -o \
+// RUN:     %t/MyVec-Type.pcm -triple=x86_64-linux-gnu 
+// RUN:%clang_cc1 -std=c++20 %t/Vec.cppm -emit-module-interface -o \
+// RUN:     %t/MyVec-Vec.pcm -fmodule-file=MyVec:Type=%t/MyVec-Type.pcm \
+// RUN:     -triple=x86_64-linux-gnu 
+// RUN: %clang_cc1 -std=c++20 %t/Vec2.cppm -emit-module-interface -o \
+// RUN:     %t/MyVec-Vec2.pcm -fmodule-file=MyVec:Type=%t/MyVec-Type.pcm \
+// RUN:     -triple=x86_64-linux-gnu 
+// RUN: %clang_cc1 -std=c++20 %t/Calculator.cppm -emit-module-interface -o \
+// RUN:     %t/MyVec-Calculator.pcm -fmodule-file=MyVec:Vec=%t/MyVec-Vec.pcm   \
+// RUN:     -fmodule-file=MyVec:Vec2=%t/MyVec-Vec2.pcm \
+// RUN:     -fmodule-file=MyVec:Type=%t/MyVec-Type.pcm \
+// RUN:     -triple=x86_64-linux-gnu 
+// RUN: %clang_cc1 -std=c++20 %t/MyVec-Calculator.pcm -S -emit-llvm \
+// RUN:     -fmodule-file=MyVec:Vec=%t/MyVec-Vec.pcm   \
+// RUN:     -fmodule-file=MyVec:Vec2=%t/MyVec-Vec2.pcm \
+// RUN:     -fmodule-file=MyVec:Type=%t/MyVec-Type.pcm \
+// RUN:     -triple=x86_64-linux-gnu -o - \
+// RUN:     | FileCheck %t/Calculator.cppm
+
+//--- Type.cppm
+export module MyVec:Type;
+
+template <class T> struct Size {
+  auto total() const { return 1; }
+};
+
+//--- Vec.cppm
+export module MyVec:Vec;
+import :Type;
+
+int size_ = Size<int>().total();
+
+//--- Vec2.cppm
+export module MyVec:Vec2;
+import :Type;
+
+struct Vec2 {
+    Size<int> size_;
+};
+
+//--- Calculator.cppm
+export module MyVec:Calculator;
+
+import :Vec;
+import :Vec2;
+
+auto Calculate() { return Size<int>().total(); };
+
+// Check the emitted module initializer to make sure we generate the module unit
+// successfully.
+// CHECK: @_ZW5MyVec9Calculatev