diff --git a/src/maasserver/rpc/boot.py b/src/maasserver/rpc/boot.py
index 2eae1db66..f2eac4f26 100644
--- a/src/maasserver/rpc/boot.py
+++ b/src/maasserver/rpc/boot.py
@@ -235,7 +235,10 @@ def get_boot_config_for_machine(machine, configs, purpose):
                 if install_image.base_image is not None:
                     # if the operating system is a custom ubuntu image,
                     # use the base image to install
-                    osystem, series = install_image.base_image.split("/")
+                    if "/" not in install_image.base_image:
+                        series = install_image.base_image
+                    else:
+                        osystem, series = install_image.base_image.split("/")
 
             if install_image is None or osystem != "ubuntu":
                 # Use only the commissioning osystem and series, for operating