diff --git a/tools/flash.sh b/tools/flash.sh
index 13ef62a..a7c8ec7 100755
--- a/tools/flash.sh
+++ b/tools/flash.sh
@@ -6,6 +6,8 @@ set -euo pipefail
 DEV=${1:?usage: tools/flash.sh <device> <port> [full]}
 PORT=${2:?usage: tools/flash.sh <device> <port> [full]}
 MODE=${3:-app}
+# wm_tool prepends /dev/ itself - accept either spelling.
+PORT=${PORT#/dev/}
 ROOT=$(cd "$(dirname "$0")/.." && pwd)
 TOOL="$ROOT/build/host-tools/wm_tool"
 if [ ! -x "$TOOL" ] || [ "$ROOT/sdk/tools/wm_tool.c" -nt "$TOOL" ]; then