diff --git a/null.v b/null.v
index 257547f..46d40b4 100644
--- a/null.v
+++ b/null.v
@@ -19,7 +19,7 @@ pub fn (c &NullCollector) counters() []Metric {
 	return []
 }
 
-pub fn (mut c DefaultCollector) histogram_buckets_set(name string, buckets []f64) {}
+pub fn (c &NullCollector) histogram_buckets_set(name string, buckets []f64) {}
 
 pub fn (c &NullCollector) histogram_record(value f64, metric Metric) {}