diff --git a/slides/Dockerfile b/slides/Dockerfile
index c9390edb..491b015f 100644
--- a/slides/Dockerfile
+++ b/slides/Dockerfile
@@ -1,7 +1,4 @@
-FROM alpine
-RUN apk update
-RUN apk add entr
-RUN apk add py-pip
-RUN apk add git
+FROM alpine:3.9
+RUN apk add --no-cache entr py-pip git
 COPY requirements.txt .
 RUN pip install -r requirements.txt