diff --git a/appimage/Dockerfile b/appimage/Dockerfile
index da0b8b72..c1914144 100644
--- a/appimage/Dockerfile
+++ b/appimage/Dockerfile
@@ -1,28 +1,13 @@
-FROM ubuntu:18.04 as start
+FROM ubuntu:20.04
 ENV DEBIAN_FRONTEND=noninteractive
 RUN apt-get update
 RUN apt-get -y install screen git sudo \
-    build-essential pkg-config \
+    build-essential pkg-config cmake \
     zlib1g-dev libjpeg-dev libgnutls28-dev \
     python3-pip texlive-latex-extra latexmk \
-    inkscape imagemagick busybox-static wget fuse
-
-# Until we move to ubuntu:20.04, we need a newer cmake. After 20.04,
-# we can remove this and add cmake to the install above.
-RUN apt-get -y install software-properties-common wget
-RUN wget -O /etc/apt/trusted.gpg.d/kitware.asc \
-    https://apt.kitware.com/keys/kitware-archive-latest.asc
-RUN apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main'
-RUN apt-get update
-RUN apt-get -y install cmake
-# End cmake
-
-RUN apt-get clean && rm -rf /var/lib/apt/lists/*
-
+    inkscape imagemagick busybox-static wget fuse && \
+    apt-get clean && rm -rf /var/lib/apt/lists/*
 RUN pip3 install sphinx sphinx_rtd_theme
-
-FROM ubuntu:18.04 as run
-COPY --from=start / /
 COPY entrypoint /entrypoint
 RUN chmod +x /entrypoint
 ENTRYPOINT [ "/entrypoint" ]
diff --git a/appimage/build-appimage b/appimage/build-appimage
index 8cad9f1f..6ee016e0 100755
--- a/appimage/build-appimage
+++ b/appimage/build-appimage
@@ -47,14 +47,14 @@ fi
 _osversion=$(cat /etc/os-release | grep PRETTY_NAME | awk -F'=' '{print $2}' | sed 's#"##g')
 
 # Warn users building the AppImage locally:
-if [[ ! $_osversion =~ Ubuntu\ 18.04.*\ LTS ]]; then
+if [[ ! $_osversion =~ Ubuntu\ 20.04.*\ LTS ]]; then
 set +x
     echo ""
     #    0         1         2         3         4         5         6         7
     #    01234567890123456789012345678901234567890123456789012345678901234567890123456789
     echo "+===========================================================================+"
     echo "|| WARNING: You are about to build a QPDF AppImage on a system which is    ||"
-    echo "|| NOT Ubuntu 18.04 LTS.                                                   ||"
+    echo "|| NOT Ubuntu 20.04 LTS.                                                   ||"
     echo "||                                                                         ||"
     echo "||    It is recommended that you use a distribution that is at least a     ||"
     echo "||    few years old to maximize the number of Linux distributions the      ||"