diff --git a/check-missing-functions b/check-missing-functions
new file mode 100755
index 0000000..a76aefc
--- /dev/null
+++ b/check-missing-functions
@@ -0,0 +1,13 @@
+#!/bin/sh
+
+set -e
+
+# functions already in src/proxmox-acme
+PRESENT=$(awk 'BEGIN{ORS="|";} /^_/{ gsub(/\(\) {/, ""); print $0}' \
+	src/proxmox-acme | sed -r 's/\|$//')
+# functions defined in all plugins
+LOCAL=$(awk 'BEGIN{ORS="|";} /^_/{ gsub(/\(\) {/, ""); print $0}' \
+	src/acme.sh/dnsapi/dns*.sh | sed -r 's/\|$//')
+
+grep -E '\b_[a-zA-Z0-9_-]+ ' src/acme.sh/dnsapi/dns_*sh | \
+	grep -Ev "$PRESENT|$LOCAL|\b_[a-zA-Z0-9_-]+=|^src/acme.sh/dnsapi/.*sh: *#"