diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 7f9eabb3ee32268cfe17b0595622566e54bc68e0..259b6021ca630d3dd33ac33001ed7926da5ea91b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,4 +1,4 @@
-image: beagle/debian-build:latest
+image: beagle/sphinx-build-env:latest
 
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
@@ -6,6 +6,7 @@ variables:
 cache:
   paths:
   - .venv
+  - .cache
 
 build:
   stage: build
@@ -18,7 +19,6 @@ build:
     paths:
     - public/$TARGET
   before_script:
-    - apt update && apt install -y python3-venv doxygen
     - source ./venv-build-env.sh
   script:
     - ./gitlab-build.sh $TARGET
diff --git a/gitlab-build.sh b/gitlab-build.sh
index 93643e370176c1ba1d983405c40d3ba7d0e29ebc..6518dbd6a1100c103c45115abf24a5a5391e78b6 100755
--- a/gitlab-build.sh
+++ b/gitlab-build.sh
@@ -48,13 +48,13 @@ HERE
 
 		echo "**** make html ****"
 		# Build HTML
-		make html -j$(nproc) BUILDDIR=public
+		make html BUILDDIR=public
 	fi
 
 	if [ "x$1" == "xpdf" ]; then
 		echo "**** make latexpdf ****"
 		# Build, optimize, and serve PDF
-		make latexpdf -j$(nproc) BUILDDIR=public
+		make latexpdf BUILDDIR=public
 
 		echo "**** pdfcpu ****"
 		pdfcpu version