diff --git a/docker/zisk/Dockerfile.cluster b/docker/zisk/Dockerfile.cluster
index db57f0a2..9fb20f6b 100644
--- a/docker/zisk/Dockerfile.cluster
+++ b/docker/zisk/Dockerfile.cluster
@@ -57,8 +57,11 @@ ARG CUDA
 # Default to build for RTX 50 series
 ARG CUDA_ARCH=sm_120
 
-# Build binaries
-RUN cargo build --release ${CUDA:+--features gpu}
+# Strip the sm_ prefix and export as CUDA_ARCHS (plural, numeric) which is the
+# env var proofman-starks-lib-c/build.rs reads to generate nvcc -gencode flags.
+# See note in docker/zisk/Dockerfile.server for full rationale.
+RUN CUDA_ARCHS="${CUDA_ARCH#sm_}" \
+    cargo build --release ${CUDA:+--features gpu}
 
 FROM $RUNTIME_IMAGE AS runtime
 FROM $RUNTIME_CUDA_IMAGE AS runtime_cuda
diff --git a/docker/zisk/Dockerfile.server b/docker/zisk/Dockerfile.server
index aceff040..d314431f 100644
--- a/docker/zisk/Dockerfile.server
+++ b/docker/zisk/Dockerfile.server
@@ -17,7 +17,14 @@ ARG RUSTFLAGS
 # Default to build for RTX 50 series
 ARG CUDA_ARCH=sm_120
 
-RUN cargo build --release --package ere-server --bin ere-server --features zisk${CUDA:+,cuda} \
+# Strip the sm_ prefix and export as CUDA_ARCHS (plural, numeric) which is the
+# env var proofman-starks-lib-c/build.rs reads to generate nvcc -gencode flags.
+# Without this export, CUDA_ARCH is declared-but-unused and the build silently
+# falls back to the committed sm_120 default in pil2-stark's CudaArch.mk,
+# producing an image that fails on any non-sm_120 GPU with CUDA error 209
+# (no kernel image is available for execution on the device).
+RUN CUDA_ARCHS="${CUDA_ARCH#sm_}" \
+    cargo build --release --package ere-server --bin ere-server --features zisk${CUDA:+,cuda} \
     && mkdir bin && mv target/release/ere-server bin/ere-server \
     && cargo clean && rm -rf $CARGO_HOME/registry/