Index: clang-tools-extra/clang-tidy/cppcoreguidelines/SpecialMemberFunctionsCheck.h
===================================================================
--- clang-tools-extra/clang-tidy/cppcoreguidelines/SpecialMemberFunctionsCheck.h
+++ clang-tools-extra/clang-tidy/cppcoreguidelines/SpecialMemberFunctionsCheck.h
@@ -31,7 +31,7 @@
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
   void onEndOfTranslationUnit() override;
 
-  enum class SpecialMemberFunctionKind {
+  enum class SpecialMemberFunctionKind : uint8_t {
     Destructor,
     CopyConstructor,
     CopyAssignment,
@@ -43,9 +43,9 @@
 
   using ClassDefiningSpecialMembersMap =
       llvm::DenseMap<ClassDefId,
-                     llvm::SmallSetVector<SpecialMemberFunctionKind, 5>>;
+                     llvm::SmallVector<SpecialMemberFunctionKind, 5>>;
 
-private:
+ private:
   ClassDefiningSpecialMembersMap ClassWithSpecialMembers;
 };
 
Index: clang-tools-extra/clang-tidy/cppcoreguidelines/SpecialMemberFunctionsCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/cppcoreguidelines/SpecialMemberFunctionsCheck.cpp
+++ clang-tools-extra/clang-tidy/cppcoreguidelines/SpecialMemberFunctionsCheck.cpp
@@ -97,8 +97,11 @@
                   {"move-assign", SpecialMemberFunctionKind::MoveAssignment}};
 
   for (const auto &KV : Matchers)
-    if (Result.Nodes.getNodeAs<CXXMethodDecl>(KV.first))
-      ClassWithSpecialMembers[ID].insert(KV.second);
+    if (Result.Nodes.getNodeAs<CXXMethodDecl>(KV.first)) {
+      SpecialMemberFunctionKind Kind = KV.second;
+      auto &Members = ClassWithSpecialMembers[ID];
+      if (find(Members, Kind) == Members.end()) Members.push_back(Kind);
+    }
 }
 
 void SpecialMemberFunctionsCheck::onEndOfTranslationUnit() {
@@ -125,7 +128,7 @@
                         std::back_inserter(UndefinedSpecialMembers));
 
     diag(C.first.first, "class '%0' defines %1 but does not define %2")
-        << C.first.second << join(DefinedSpecialMembers.getArrayRef(), " and ")
+        << C.first.second << join(DefinedSpecialMembers, " and ")
         << join(UndefinedSpecialMembers, " or ");
   }
 }