diff --git a/Dockerfile.ci b/Dockerfile.ci
index 785cfd81..d73fd2a6 100644
--- a/Dockerfile.ci
+++ b/Dockerfile.ci
@@ -31,16 +31,16 @@ WORKDIR /tmp/exla_warm
 COPY mix.exs mix.lock /tmp/exla_warm/
 COPY vendor /tmp/exla_warm/vendor
 
+# Minimal config — nx needs :default_backend to exist.
+# Set :exla make_args to -j1 so C++ compiles serially (the default
+# nproc-2 can cause parallel OOM kills on CI runners).
 RUN mkdir -p /tmp/exla_warm/config && \
-    printf 'import Config\nconfig :nx, :default_backend, EXLA.Backend\n' > /tmp/exla_warm/config/config.exs
+    printf 'import Config\nconfig :nx, :default_backend, EXLA.Backend\nconfig :exla, :make_args, ["-j1"]\n' > /tmp/exla_warm/config/config.exs
 
 # Compile all deps. EXLA's Makefile defaults to -O3 which OOM-kills g++
 # on low-memory CI runners. Patch it to -O0 before compilation.
-# Also override make_args to -j1 (EXLA defaults to nproc-2 parallel jobs)
-# since elixir_make's sanitized env blocks MAKEFLAGS/DEBUG from reaching make.
 RUN mix deps.get && \
     sed -i 's/-O3/-O0/g' deps/exla/Makefile && \
-    mix run -e 'Application.put_env(:exla, :make_args, ["-j1"])' && \
     mix deps.compile
 
 # Save the full build cache (libexla.so + .o files + xla_extension lib)