diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index f0bbcdf5..75829676 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -17,8 +17,9 @@ jobs:
             #- macos-latest
             #- windows-latest
         ocaml-compiler:
-          - 4.05
-          - 4.14
+          - 4.08.x
+          - 4.14.x
+          - 5.1.x
 
     runs-on: ${{ matrix.os }}
 
diff --git a/dune-project b/dune-project
index 95927d24..435b7f75 100644
--- a/dune-project
+++ b/dune-project
@@ -19,7 +19,7 @@
     seq
     base-threads
     result
-    (ocaml (>= 4.05))
+    (ocaml (>= 4.08))
     (odoc :with-doc)
     (conf-libcurl :with-test)
     (ptime :with-test)
diff --git a/src/prometheus/tiny_httpd_prometheus.ml b/src/prometheus/tiny_httpd_prometheus.ml
index 37a968cf..dcc19a8b 100644
--- a/src/prometheus/tiny_httpd_prometheus.ml
+++ b/src/prometheus/tiny_httpd_prometheus.ml
@@ -102,7 +102,7 @@ module Histogram = struct
   let create reg ?(tags = []) ?descr ~buckets name : t =
     opt_iter_ (validate_descr_ "histogram") descr;
     let buckets =
-      List.sort Float.compare buckets
+      List.sort Stdlib.compare buckets
       |> List.map (fun thresh -> thresh, A.make 0)
     in
     let buckets = Array.of_list @@ buckets @ [ infinity, A.make 0 ] in
diff --git a/tiny_httpd.opam b/tiny_httpd.opam
index 6a2d337b..955a14fe 100644
--- a/tiny_httpd.opam
+++ b/tiny_httpd.opam
@@ -15,7 +15,7 @@ depends: [
   "seq"
   "base-threads"
   "result"
-  "ocaml" {>= "4.05"}
+  "ocaml" {>= "4.08"}
   "odoc" {with-doc}
   "conf-libcurl" {with-test}
   "ptime" {with-test}