diff --git a/src/compiler/sema_decls.c b/src/compiler/sema_decls.c
index e4388bb04..ae218449c 100755
--- a/src/compiler/sema_decls.c
+++ b/src/compiler/sema_decls.c
@@ -3262,7 +3262,7 @@ static bool sema_analyse_attribute(SemaContext *context, ResolvedAttrData *attr_
 			}
 			return true;
 			FAILED_OP_TYPE:
-			RETURN_SEMA_ERROR(attr, "'operator' requires an operator type argument: '[]', '[]=', '&[]' or 'len'.");
+			RETURN_SEMA_ERROR(attr, "'operator' requires an operator type argument. It should be any of the arithmetic and bit operators, equality operators, '[]', '[]=', '&[]' or 'len'.");
 		}
 		case ATTRIBUTE_ALIGN:
 			if (!expr)