diff --git a/quic/interop/Makefile b/quic/interop/Makefile
index 1eb26eec8..5e7f97ae6 100644
--- a/quic/interop/Makefile
+++ b/quic/interop/Makefile
@@ -38,6 +38,7 @@ smoke: docker smoke-down
 	@echo "picoquic up on $(SMOKE_PICOQUIC):4433 (in $(SMOKE_NET))"
 	docker run --rm --name $(SMOKE_CLIENT) \
 	    --network $(SMOKE_NET) \
+	    -e SMOKE_MODE=1 \
 	    -e ROLE=client \
 	    -e TESTCASE=handshake \
 	    -e REQUESTS="https://$(SMOKE_PICOQUIC):4433/" \
diff --git a/quic/interop/run_endpoint.sh b/quic/interop/run_endpoint.sh
index 4fc33b9c1..521d52be7 100755
--- a/quic/interop/run_endpoint.sh
+++ b/quic/interop/run_endpoint.sh
@@ -2,15 +2,19 @@
 # quic-interop-runner endpoint entry point.
 #
 # The base image (martenseemann/quic-network-simulator-endpoint) provides
-# /setup.sh, which configures routing for the runner's ns-3 sim. We try
-# to source it but tolerate failure so smoke tests outside the runner
-# (without --privileged / the sim's network) still launch the JVM client.
-# Inside the runner, /setup.sh succeeds because the runner provides the
-# necessary capabilities.
+# /setup.sh, which configures routing for the runner's ns-3 sim. We source
+# it inside the runner — but for `make smoke` runs against a plain Docker
+# bridge network, sourcing /setup.sh succeeds AND breaks DNS resolution
+# (it points the resolver at the sim's nameserver which doesn't exist
+# in smoke mode). Set SMOKE_MODE=1 to skip /setup.sh entirely.
 set -uo pipefail
 
-# shellcheck disable=SC1091
-source /setup.sh 2>/dev/null || echo "(setup.sh skipped — running outside the runner sim)" >&2
+if [ "${SMOKE_MODE:-0}" = "1" ]; then
+    echo "(smoke mode — skipping /setup.sh, using container default networking)" >&2
+else
+    # shellcheck disable=SC1091
+    source /setup.sh 2>/dev/null || echo "(setup.sh skipped — running outside the runner sim)" >&2
+fi
 
 set -e