diff --git a/nixos/modules/virtualisation/nixos-containers.nix b/nixos/modules/virtualisation/nixos-containers.nix
index dc53276edacd..9b595b030024 100644
--- a/nixos/modules/virtualisation/nixos-containers.nix
+++ b/nixos/modules/virtualisation/nixos-containers.nix
@@ -526,7 +526,7 @@ let
 
   # Parses an IP address with an optional prefix
   ipFromString =
-    str:
+    str: defaultPrefix:
     let
       segments = lib.splitString "/" str;
       prefix = lib.elemAt segments 1;
@@ -534,7 +534,7 @@ let
     in
     {
       address = lib.head segments;
-      prefixLength = if hasPrefix then builtins.fromJSON prefix else 32;
+      prefixLength = if hasPrefix then builtins.fromJSON prefix else defaultPrefix;
     };
 
 in
@@ -610,10 +610,10 @@ in
                                 networking.interfaces = lib.mkIf config.privateNetwork (
                                   lib.mkMerge [
                                     (lib.mkIf (config.localAddress != null) {
-                                      eth0.ipv4.addresses = [ (ipFromString config.localAddress) ];
+                                      eth0.ipv4.addresses = [ (ipFromString config.localAddress 32) ];
                                     })
                                     (lib.mkIf (config.localAddress6 != null) {
-                                      eth0.ipv6.addresses = [ (ipFromString config.localAddress6) ];
+                                      eth0.ipv6.addresses = [ (ipFromString config.localAddress6 128) ];
                                     })
                                   ]
                                 );