diff --git a/docker/Dockerfile_ubuntu_18.04 b/docker/Dockerfile_ubuntu_18.04
index 7eaec5585fa128a3237eea546233940041f9d0cf..95ad7ddd0f04ed37bf2e00b8f607bfce147e4969 100644
--- a/docker/Dockerfile_ubuntu_18.04
+++ b/docker/Dockerfile_ubuntu_18.04
@@ -11,6 +11,12 @@ RUN apt-get update && \
         g++-8 \
         wget
 
+# FindPythonInterp in CMake < 3.12 is buggy; install 3.12.
+RUN wget https://cmake.org/files/v3.12/cmake-3.12.0-Linux-x86_64.tar.gz && \
+    echo "2cc891a77f5850ffecb2d358f3a84cd9b90e6941496ca531ea31e7bd7600a373  \
+cmake-3.12.0-Linux-x86_64.tar.gz" | sha256sum --check && \
+    tar xf cmake-3.12.0-Linux-x86_64.tar.gz --strip-components=1 -C /usr/local
+
 ADD scripts/prebuild-package-debian.sh /opt/prebuild-package-debian.sh
 
 COPY packaging/rules/debian-qt/control /tmp/builddeps/debian/control