diff --git a/Dockerfile b/Dockerfile
index 791a922..750f674 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,7 +2,7 @@
 ###############################
 # Build the doctree Go binary #
 ###############################
-FROM golang:1.18-alpine as builder
+FROM golang:1.18-alpine@sha256:77f25981bd57e60a510165f3be89c901aec90453fd0f1c5a45691f6cb1528807 as builder
 
 RUN apk add --no-cache git build-base
 COPY . /doctree