diff --git a/vlib/v/gen/js/tests/js.v b/vlib/v/gen/js/tests/js.v
index 4aac31f8593cca..090aaee5acd9f7 100644
--- a/vlib/v/gen/js/tests/js.v
+++ b/vlib/v/gen/js/tests/js.v
@@ -146,7 +146,7 @@ fn error_if_even(num int) !int {
 	return num
 }
 
-fn propagation() ? {
+fn propagation() ! {
 	println('Propagation test:')
 	return error('"Task failed successfully" - Windows XP')
 }
diff --git a/vlib/v/gen/js/tests/option.v b/vlib/v/gen/js/tests/option.v
index f2dc999ab42bb6..24314f616b2e88 100644
--- a/vlib/v/gen/js/tests/option.v
+++ b/vlib/v/gen/js/tests/option.v
@@ -16,14 +16,14 @@ fn try_numbers() ? {
 	}
 }
 
-fn error_if_even(num int) ?int {
+fn error_if_even(num int) !int {
 	if num % 2 == 0 {
 		return error('number is even')
 	}
 	return num
 }
 
-fn error_if_prime(num int) ?int {
+fn error_if_prime(num int) !int {
 	for i in 2 .. num {
 		if num % i == 0 {
 			return error('${num} is prime')