diff --git a/Dockerfile b/Dockerfile
index 791a922..83c27b6 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:dda10a0c69473a595ab11ed3f8305bf4d38e0436b80e1462fb22c9d8a1c1e808 as builder
 
 RUN apk add --no-cache git build-base
 COPY . /doctree