diff --git a/Dockerfile.ci b/Dockerfile.ci
index 1cb36852..785cfd81 100644
--- a/Dockerfile.ci
+++ b/Dockerfile.ci
@@ -34,11 +34,14 @@ COPY vendor /tmp/exla_warm/vendor
 RUN mkdir -p /tmp/exla_warm/config && \
     printf 'import Config\nconfig :nx, :default_backend, EXLA.Backend\n' > /tmp/exla_warm/config/config.exs
 
-# Compile all deps. DEBUG=1 tells the EXLA Makefile to use -g instead
-# of -O3 — this avoids the heavy optimization passes that OOM-kill g++
-# on low-memory CI runners. MAKEFLAGS=-j1 serializes make jobs. The
-# resulting unoptimized NIF is fine for tests.
-RUN MAKEFLAGS="-j1" DEBUG=1 mix deps.get && MAKEFLAGS="-j1" DEBUG=1 mix deps.compile
+# 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)
 # so Make finds all targets already built when restored in the test step.