diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 24b9d92f57..f416eb9abf 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -186,10 +186,10 @@ fn new_array_from_c_array_no_alloc(len int, cap int, elm_size int, c_array voidp
 	return arr
 }
 
-// Private function. Increases the `cap` of an array to the
-// required value by copying the data to a new memory location
-// (creating a clone) unless `a.cap` is already large enough.
-fn (mut a array) ensure_cap(required int) {
+// ensure_cap increases the `cap` of an array to the required value
+// by copying the data to a new memory location (creating a clone),
+// unless `a.cap` is already large enough.
+pub fn (mut a array) ensure_cap(required int) {
 	if required <= a.cap {
 		return
 	}
diff --git a/vlib/strings/builder_test.v b/vlib/strings/builder_test.v
index 9ca8c354e7..a981950e2c 100644
--- a/vlib/strings/builder_test.v
+++ b/vlib/strings/builder_test.v
@@ -183,7 +183,7 @@ fn test_grow_len() {
 	assert sb.len == 20
 	assert sb.cap == 20
 
-	unsafe { sb.ensure_cap(35) }
+	sb.ensure_cap(35)
 	assert sb.len == 20
 	assert sb.cap == 35