Index: clang/lib/Sema/SemaDecl.cpp =================================================================== --- clang/lib/Sema/SemaDecl.cpp +++ clang/lib/Sema/SemaDecl.cpp @@ -13916,7 +13916,8 @@ Invalid = true; } - if (!Invalid && TUK == TUK_Definition && DC->getDeclKind() == Decl::Enum) { + if (!Invalid && getLangOpts().CPlusPlus && TUK == TUK_Definition && + DC->getDeclKind() == Decl::Enum) { Diag(New->getLocation(), diag::err_type_defined_in_enum) << Context.getTagDeclType(New); Invalid = true; Index: clang/test/Sema/enum.c =================================================================== --- clang/test/Sema/enum.c +++ clang/test/Sema/enum.c @@ -125,9 +125,10 @@ typedef struct Color NewColor; // expected-error {{use of 'Color' with tag type that does not match previous declaration}} // PR28903 +// In C it is valid to define tags inside enums. struct PR28903 { enum { - PR28903_A = (enum { // expected-error-re {{'enum PR28903::(anonymous at {{.*}})' cannot be defined in an enumeration}} + PR28903_A = (enum { PR28903_B, PR28903_C = PR28903_B })0