diff --git a/src/ci/docker/host-x86_64/optional-x86_64-gnu-parallel-frontend/Dockerfile b/src/ci/docker/host-x86_64/optional-x86_64-gnu-parallel-frontend/Dockerfile
index 8f7c7ebe35559..9996c17aaa4b3 100644
--- a/src/ci/docker/host-x86_64/optional-x86_64-gnu-parallel-frontend/Dockerfile
+++ b/src/ci/docker/host-x86_64/optional-x86_64-gnu-parallel-frontend/Dockerfile
@@ -31,6 +31,8 @@ ENV RUST_CONFIGURE_ARGS \
  --enable-compiler-docs \
  --set llvm.libzstd=true
 
+# Compile each test sequentially to achieve max thread utilization by a single rustc process
+ENV RUST_TEST_THREADS 1
+
 # Build the toolchain with multiple parallel frontend threads and then run tests
-# Tests are still compiled serially at the moment (intended to be changed in follow-ups).
-ENV SCRIPT python3 ../x.py --stage 2 test --set rust.parallel-frontend-threads=4
+ENV SCRIPT python3 ../x.py --stage 2 test --set rust.parallel-frontend-threads=4 "--" --parallel-frontend-threads=4 --iteration-count=2