Index: clang-tidy/utils/TypeTraits.cpp
===================================================================
--- clang-tidy/utils/TypeTraits.cpp
+++ clang-tidy/utils/TypeTraits.cpp
@@ -41,7 +41,7 @@
 
 llvm::Optional<bool> isExpensiveToCopy(QualType Type,
                                        const ASTContext &Context) {
-  if (Type->isDependentType())
+  if (Type->isDependentType() || Type->isIncompleteType())
     return llvm::None;
   return !Type.isTriviallyCopyableType(Context) &&
          !classHasTrivialCopyAndDestroy(Type) &&