diff --git a/prometheus.scm b/prometheus.scm
index b1b3d31..04f24d8 100644
--- a/prometheus.scm
+++ b/prometheus.scm
@@ -32,6 +32,11 @@
 
             make-counter-metric
             make-gauge-metric
+
+            %default-histogram-buckets
+            linear-histogram-buckets
+            exponential-histogram-buckets
+
             make-histogram-metric
 
             metric-increment