diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -3734,9 +3734,14 @@
 
   // Connect the redecl chain.
   if (FoundByLookup) {
-    auto *Recent = const_cast<FunctionDecl *>(
-          FoundByLookup->getMostRecentDecl());
-    ToFunction->setPreviousDecl(Recent);
+    if (auto *Ctor = dyn_cast<CXXConstructorDecl>(D);
+        Ctor && Ctor->isImplicit())
+      DC->removeDecl(FoundByLookup);
+    else {
+      auto *Recent =
+          const_cast<FunctionDecl *>(FoundByLookup->getMostRecentDecl());
+      ToFunction->setPreviousDecl(Recent);
+    }
     // FIXME Probably we should merge exception specifications.  E.g. In the
     // "To" context the existing function may have exception specification with
     // noexcept-unevaluated, while the newly imported function may have an
diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -3175,6 +3175,39 @@
   testNoImportOf(cxxMethodDecl(hasName("f")), Code);
 }
 
+TEST_P(ImportImplicitMethods, MergeImplicitMethodWithDefinition) {
+  Decl *From, *To;
+  std::tie(From, To) = getImportedDecl(
+      R"s(
+        struct A {
+          A() : m() {}
+          int m;
+        };
+
+        A foo() { A a; return a; }
+        A bar() { return {}; }
+      )s",
+      Lang_CXX17,
+      R"s(
+        struct A {
+          A() : m() {}
+          int m;
+        };
+        A baz() { return {}; }
+      )s",
+      Lang_CXX17, "A");
+
+  MatchVerifier<Decl> Verifier;
+  auto HasCopyCtor = has(cxxConstructorDecl(isCopyConstructor(), isImplicit()));
+  auto HasCtorInit =
+      hasAnyConstructorInitializer(cxxCtorInitializer(isMemberInitializer()));
+  auto HasMoveCtor =
+      has(cxxConstructorDecl(isMoveConstructor(), isImplicit(), HasCtorInit));
+  auto Pattern = cxxRecordDecl(HasCopyCtor, HasMoveCtor);
+  ASSERT_TRUE(Verifier.match(From, Pattern));
+  EXPECT_TRUE(Verifier.match(To, Pattern));
+}
+
 TEST_P(ASTImporterOptionSpecificTestBase, ImportOfEquivalentRecord) {
   Decl *ToR1;
   {