Try making the base image tag specifiable

server-ce/Dockerfile

@@ -2,7 +2,8 @@
 # Overleaf Community Edition (overleaf/overleaf)
 # ---------------------------------------------
 
-FROM sharelatex/sharelatex-base:latest
+ARG SHARELATEX_BASE_TAG=sharelatex/sharelatex-base:latest
+FROM $SHARELATEX_BASE_TAG
 
 ENV SHARELATEX_CONFIG /etc/sharelatex/settings.coffee
 

server-ce/Makefile

@@ -8,7 +8,7 @@ build-base:
 
 
 build-community:
-	docker build -f Dockerfile -t $(SHARELATEX_TAG) .
+	docker build --build-arg SHARELATEX_BASE_TAG=$(SHARELATEX_BASE_TAG) -f Dockerfile -t $(SHARELATEX_TAG) .
 
 
 PHONY: build-base build-community