diff --git a/tests/docker/dockerfiles/debian-tricore-cross.docker b/tests/docker/dockerfiles/debian-tricore-cross.docker
index 34b2cea4e3..5ae58efa09 100644
--- a/tests/docker/dockerfiles/debian-tricore-cross.docker
+++ b/tests/docker/dockerfiles/debian-tricore-cross.docker
@@ -20,6 +20,7 @@ RUN apt update && \
        bzip2 \
        ca-certificates \
        ccache \
+       flex \
        g++ \
        gcc \
        git \