diff --git a/.github/ci/doc.sh b/.github/ci/doc.sh
index e4d83e4b..9e9c78a4 100755
--- a/.github/ci/doc.sh
+++ b/.github/ci/doc.sh
@@ -6,7 +6,7 @@ set -euo pipefail
 export RUSTUP_HOME=/ci/cache/rustup
 export CARGO_HOME=/ci/cache/cargo
 export CARGO_TARGET_DIR=/ci/cache/target
-export BUILDER_THREADS=6
+export BUILDER_THREADS=4
 export BUILDER_COMPRESS=true
 
 # force rustup to download the toolchain before starting building.