diff --git a/vlib/builtin/map.v b/vlib/builtin/map.v
index 7b96d124af..71ad5275af 100644
--- a/vlib/builtin/map.v
+++ b/vlib/builtin/map.v
@@ -425,6 +425,11 @@ fn (mut m map) expand() {
 // the max_load_factor in an operation.
 fn (mut m map) rehash() {
 	meta_bytes := sizeof(u32) * (m.even_index + 2 + m.extra_metas)
+	m.reserve(meta_bytes)
+}
+
+// reserve memory for the map meta data
+pub fn (mut m map) reserve(meta_bytes u32) {
 	unsafe {
 		// TODO: use realloc_data here too
 		x := v_realloc(&u8(m.metas), int(meta_bytes))