diff --git a/tests/docker/dockerfiles/ubuntu.docker b/tests/docker/dockerfiles/ubuntu.docker
index d3b72209c8..2500ec84b6 100644
--- a/tests/docker/dockerfiles/ubuntu.docker
+++ b/tests/docker/dockerfiles/ubuntu.docker
@@ -61,6 +61,7 @@ ENV PACKAGES flex bison \
     libxen-dev \
     make \
     python-yaml \
+    python3-sphinx \
     sparse \
     texinfo \
     xfslibs-dev
diff --git a/tests/docker/dockerfiles/ubuntu1804.docker b/tests/docker/dockerfiles/ubuntu1804.docker
index 9d80b11500..0bb8088658 100644
--- a/tests/docker/dockerfiles/ubuntu1804.docker
+++ b/tests/docker/dockerfiles/ubuntu1804.docker
@@ -48,6 +48,7 @@ ENV PACKAGES flex bison \
     libxen-dev \
     make \
     python-yaml \
+    python3-sphinx \
     sparse \
     texinfo \
     xfslibs-dev