diff --git a/lang/ast/expr/arith.c b/lang/ast/expr/arith.c
index 3a88436..6d798f8 100644
--- a/lang/ast/expr/arith.c
+++ b/lang/ast/expr/arith.c
@@ -739,6 +739,34 @@ not_complex_msg:
 
 	/* this is a generic parenthesis-enclosed sub-expression.
 	 * create a new sub-expr parser to handle it */
+
+	if (state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
+		/* this is an unlabeled complex message arg */
+		if (state->s_prev_token != IVY_SYM_COMMA
+		    && state->s_prev_token != IVY_SYM_LEFT_PAREN) {
+			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
+		}
+
+		struct ivy_token *empty_label = malloc(sizeof *empty_label);
+		if (!empty_label) {
+			return PARSE_RESULT(IVY_ERR_NO_MEMORY, 0);
+		}
+		memset(empty_label, 0x0, sizeof *empty_label);
+		empty_label->t_type = IVY_TOK_LABEL;
+
+		b_queue_push_back(&state->s_labels, &empty_label->t_entry);
+
+		struct expr_parser_state *arg_expr
+			= (struct expr_parser_state *)parser_push_state(
+				ctx, IVY_AST_EXPR, 0);
+		expr_copy_terminators(state, arg_expr);
+		expr_add_terminator(arg_expr, IVY_SYM_COMMA);
+		arg_expr->s_sub_type = EXPR_SUBTYPE_COMPLEX_ARG;
+		arg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;
+
+		return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
+	}
+
 	struct expr_parser_state *sub_expr
 		= (struct expr_parser_state *)parser_push_state(
 			ctx, IVY_AST_EXPR, 0);