diff --git a/run-ai-image.sh b/run-ai-image.sh
index 2b59137..e349575 100755
--- a/run-ai-image.sh
+++ b/run-ai-image.sh
@@ -10,6 +10,7 @@ cd "$(dirname "$0")"
 [ -f .ai-config ] || { echo "No .ai-config yet - run ./setup.sh first." >&2; exit 1; }
 # shellcheck disable=SC1091
 source .ai-config
+PORT=${AI_PORT:-$PORT}   # override for one run: AI_PORT=11500 ./run-ai-image.sh
 
 running() { [ "$(docker inspect -f '{{.State.Running}}' "$CONTAINER_NAME" 2>/dev/null)" = "true" ]; }
 exists()  { docker inspect "$CONTAINER_NAME" >/dev/null 2>&1; }
@@ -28,6 +29,12 @@ if running; then
   echo "Already running on http://127.0.0.1:$PORT"
 else
   exists && docker rm -f "$CONTAINER_NAME" >/dev/null
+  if (exec 3<>"/dev/tcp/127.0.0.1/$PORT") 2>/dev/null; then
+    echo "Port $PORT is already in use by something else (a host Ollama, another container?):" >&2
+    docker ps --filter "publish=$PORT" --format '  container {{.Names}}' >&2 || true
+    echo "Re-run ./setup.sh to pick a free port, or use: AI_PORT=<free port> ./run-ai-image.sh" >&2
+    exit 1
+  fi
   args=(-d --name "$CONTAINER_NAME" -p "127.0.0.1:$PORT:11434" --restart unless-stopped)
   [ "$USE_GPU" = "1" ] && args+=(--gpus all)
   docker run "${args[@]}" "$IMAGE_NAME" >/dev/null
diff --git a/setup.sh b/setup.sh
index ac2c394..06af0c2 100755
--- a/setup.sh
+++ b/setup.sh
@@ -4,24 +4,26 @@
 #   .ai-config   (settings used by build-ai-image.sh / run-ai-image.sh)
 #   RUN_AIDER.md (how to run aider against the container on this machine)
 #
-# Usage: ./setup.sh [--model <ollama-tag>] [--gpu|--no-gpu] [--yes]
+# Usage: ./setup.sh [--model <ollama-tag>] [--gpu|--no-gpu] [--port <n>] [--yes]
 set -euo pipefail
 cd "$(dirname "$0")"
 
-FORCE_MODEL=""; FORCE_GPU=""; ASSUME_YES=0
+FORCE_MODEL=""; FORCE_GPU=""; ASSUME_YES=0; FORCE_PORT=""
 while [ $# -gt 0 ]; do
   case "$1" in
     --model) FORCE_MODEL="${2:?--model needs a value}"; shift ;;
     --gpu) FORCE_GPU=1 ;;
     --no-gpu) FORCE_GPU=0 ;;
+    --port) FORCE_PORT="${2:?--port needs a value}"; shift ;;
     --yes|-y) ASSUME_YES=1 ;;
-    -h|--help) sed -n '2,8p' "$0" | sed 's/^# \?//'; exit 0 ;;
+    -h|--help) sed -n '2,9p' "$0" | sed 's/^# \?//'; exit 0 ;;
     *) echo "Unknown option: $1" >&2; exit 1 ;;
   esac
   shift
 done
 
-IMAGE_NAME="local-ai"; CONTAINER_NAME="local-ai"; PORT=11434
+IMAGE_NAME="local-ai"; CONTAINER_NAME="local-ai"; PORT=""
+port_busy() { (exec 3<>"/dev/tcp/127.0.0.1/$1") 2>/dev/null; }
 NOTES=()   # machine-specific remarks, echoed to the terminal and RUN_AIDER.md
 
 # Distro-specific commands to make an NVIDIA GPU usable from Docker.
@@ -219,6 +221,19 @@ if awk -v d="$sel_disk" -v f="$disk_gb" 'BEGIN{exit !(d*2>f)}'; then
   NOTES+=("Low disk space: ${disk_gb} GB free, the build needs roughly 2x the model size (${sel_disk} GB).")
 fi
 
+# ------------------------------------------------------------ host port
+# Default 11434 (Ollama's standard); if something else (e.g. a host Ollama)
+# already uses it, take the next free port.
+if [ -n "$FORCE_PORT" ]; then PORT=$FORCE_PORT
+else
+  for PORT in $(seq 11434 11534); do
+    # our own container from an earlier run doesn't count as busy
+    [ "$(docker port "$CONTAINER_NAME" 11434/tcp 2>/dev/null | head -1 | sed 's/.*://')" = "$PORT" ] && break
+    port_busy "$PORT" || break
+  done
+  [ "$PORT" != 11434 ] && NOTES+=("Port 11434 is already in use on this machine, so the AI container will use port $PORT.")
+fi
+
 # ------------------------------------------------------------------- output
 USE_GPU=$gpu_usable
 sed -e "s|@@MODEL@@|$MODEL|g" -e "s|@@CONTEXT@@|$CONTEXT|g" Dockerfile.template > Dockerfile