diff --git a/ursim/cb3/Dockerfile b/ursim/cb3/Dockerfile
index 7f504a0..e077e05 100644
--- a/ursim/cb3/Dockerfile
+++ b/ursim/cb3/Dockerfile
@@ -21,7 +21,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-FROM ubuntu:latest
+FROM ubuntu:20.04
 
 # Set Version Information
 ARG VERSION
diff --git a/ursim/e-series/Dockerfile b/ursim/e-series/Dockerfile
index 7698460..42f82dd 100644
--- a/ursim/e-series/Dockerfile
+++ b/ursim/e-series/Dockerfile
@@ -21,7 +21,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-FROM ubuntu:latest
+FROM ubuntu:20.04
 
 # Set Version Information
 ARG VERSION