diff --git a/vlib/compiler/if_match.v b/vlib/compiler/if_match.v
index 3bf7b46bab..415882fd98 100644
--- a/vlib/compiler/if_match.v
+++ b/vlib/compiler/if_match.v
@@ -235,6 +235,9 @@ fn (p mut Parser) if_statement(is_expr bool, elif_depth int) string {
 		p.check(.decl_assign)
 		p.is_var_decl = true
 		option_type, expr := p.tmp_expr()// := p.bool_expression()
+		if !option_type.starts_with('Option_') {
+			p.error('`if x := opt() {` syntax requires a function that returns an optional value')
+		}
 		p.is_var_decl = false
 		typ := option_type[7..]
 		// Option_User tmp = get_user(1);