diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c45e92202..5d5bd91b6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,7 +30,7 @@ jobs:
       BOTO_CONFIG: /dev/null
       GO111MODULE: "on"
       GOPROXY: "https://proxy.golang.org"
-      GOVER: '1.21'
+      GOVER: '1.19'
 
     steps:
       - name: Checkout repository
@@ -99,7 +99,7 @@ jobs:
           - name: Ubuntu-20
             image: "ubuntu:20.04"
             suite: focal
-            GOVER: '1.21'
+            GOVER: '1.19'
             install: "make ca-certificates git curl"
           - name: Ubuntu-22
             image: "ubuntu:22.04"
@@ -108,12 +108,12 @@ jobs:
           - name: Debian-10
             image: "debian:buster"
             suite: buster
-            GOVER: '1.21'
+            GOVER: '1.19'
             install: "make ca-certificates git curl"
           - name: Debian-11
             image: "debian:bullseye"
             suite: bullseye
-            GOVER: '1.21'
+            GOVER: '1.19'
             install: "make ca-certificates git curl"
           - name: Debian-12
             image: "debian:bookworm"
diff --git a/deb/reflist.go b/deb/reflist.go
index 55588a998..df1b9b2e6 100644
--- a/deb/reflist.go
+++ b/deb/reflist.go
@@ -428,7 +428,10 @@ func bucketRefPrefix(ref []byte) []byte {
 		ref = ref[len(libPrefix):]
 	}
 
-	prefixLen := min(maxPrefixLen, len(ref))
+	prefixLen := len(ref)
+	if maxPrefixLen < prefixLen {
+		prefixLen = maxPrefixLen
+	}
 	prefix, _, _ := bytes.Cut(ref[:prefixLen], []byte{' '})
 	return prefix
 }
@@ -715,9 +718,16 @@ func (set *RefListDigestSet) ForEach(handler func(digest []byte) error) error {
 	return nil
 }
 
+// workaround for: conversion of slices to arrays requires go1.20 or later
+func newRefListArray(digest []byte) reflistDigestArray {
+	var array reflistDigestArray
+	copy(array[:], digest)
+	return array
+}
+
 // Add adds digest to set, doing nothing if the digest was already present
 func (set *RefListDigestSet) Add(digest []byte) {
-	set.items[reflistDigestArray(digest)] = struct{}{}
+	set.items[newRefListArray(digest)] = struct{}{}
 }
 
 // AddAllInRefList adds all the bucket digests in a SplitRefList to the set
@@ -731,13 +741,13 @@ func (set *RefListDigestSet) AddAllInRefList(sl *SplitRefList) {
 
 // Has checks whether a digest is part of set
 func (set *RefListDigestSet) Has(digest []byte) bool {
-	_, ok := set.items[reflistDigestArray(digest)]
+	_, ok := set.items[newRefListArray(digest)]
 	return ok
 }
 
 // Remove removes a digest from set
 func (set *RefListDigestSet) Remove(digest []byte) {
-	delete(set.items, reflistDigestArray(digest))
+	delete(set.items, newRefListArray(digest))
 }
 
 // RemoveAll removes all the digests in other from the current set
@@ -776,10 +786,20 @@ func segmentPrefix(encodedDigest string) []byte {
 	return []byte(fmt.Sprintf("F%s-", encodedDigest))
 }
 
+// workaround for go 1.19 instead of bytes.Clone
+func cloneBytes(b []byte) []byte {
+	if b == nil {
+		return nil
+	}
+	cloned := make([]byte, len(b))
+	copy(cloned, b)
+	return cloned
+}
+
 func segmentIndexKey(prefix []byte, idx int) []byte {
 	// Assume most buckets won't have more than 0xFFFF = ~65k segments (which
 	// would be an extremely large bucket!).
-	return append(bytes.Clone(prefix), []byte(fmt.Sprintf("%04x", idx))...)
+	return append(cloneBytes(prefix), []byte(fmt.Sprintf("%04x", idx))...)
 }
 
 // AllBucketDigests returns a set of all the bucket digests in the database
@@ -861,7 +881,7 @@ func (collection *RefListCollection) loadBuckets(sl *SplitRefList) error {
 		var bucket *PackageRefList
 
 		if digest := sl.Buckets[idx]; len(digest) > 0 {
-			cacheKey := reflistDigestArray(digest)
+			cacheKey := newRefListArray(digest)
 			bucket = collection.cache[cacheKey]
 			if bucket == nil {
 				bucket = NewPackageRefList()
diff --git a/go.mod b/go.mod
index 6bdb74b18..478582cb1 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/aptly-dev/aptly
 
-go 1.21
+go 1.19
 
 require (
 	github.com/AlekSi/pointer v1.2.0
diff --git a/system/Dockerfile b/system/Dockerfile
index 3b39488e5..c22ea3155 100644
--- a/system/Dockerfile
+++ b/system/Dockerfile
@@ -2,9 +2,9 @@ FROM debian:bookworm-slim
 
 RUN apt-get update -y && apt-get install -y --no-install-recommends curl gnupg && apt-get clean && rm -rf /var/lib/apt/lists/*
 
-RUN echo deb http://deb.debian.org/debian bookworm-backports main > /etc/apt/sources.list.d/backports.list
+#RUN echo deb http://deb.debian.org/debian bookworm-backports main > /etc/apt/sources.list.d/backports.list
 RUN apt-get update && \
-    apt-get install -y --no-install-recommends apg bzip2 xz-utils ca-certificates golang/bookworm-backports golang-go/bookworm-backports golang-doc/bookworm-backports golang-src/bookworm-backports make git python3 python3-requests-unixsocket python3-termcolor python3-swiftclient python3-boto && \
+    apt-get install -y --no-install-recommends apg bzip2 xz-utils ca-certificates golang golang-go golang-doc golang-src make git python3 python3-requests-unixsocket python3-termcolor python3-swiftclient python3-boto g++ && \
     apt-get clean && rm -rf /var/lib/apt/lists/*
 
 RUN useradd -m --shell /bin/sh --home-dir /var/lib/aptly aptly