diff --git a/plugins/providers/docker/action/prepare_networks.rb b/plugins/providers/docker/action/prepare_networks.rb
index e52126f47..a61aa82e9 100644
--- a/plugins/providers/docker/action/prepare_networks.rb
+++ b/plugins/providers/docker/action/prepare_networks.rb
@@ -191,7 +191,8 @@ module VagrantPlugins
             base_opts[:opt] = "parent=#{bridge_interface.name}"
             subnet = IPAddr.new(bridge_interface.addr.ip_address <<
               "/" << bridge_interface.netmask.ip_unpack.first)
-            prefix = subnet.ipv4? ? 24 : 64
+            netmask = bridge_interface.netmask.ip_unpack.first
+            prefix = IPAddr.new("255.255.255.255/#{netmask}").to_i.to_s(2).count("1")
             base_opts[:subnet] = "#{subnet}/#{prefix}"
             subnet_addr = IPAddr.new(base_opts[:subnet])
             base_opts[:driver] = "macvlan"
@@ -214,7 +215,7 @@ module VagrantPlugins
                   network_options, bridge_interface.name, env)
               end
               network_options[:ip_range] = request_public_iprange(
-                network_options, bridge_interface.name, env)
+                network_options, bridge_interface, env)
             end
           end
           [network_name, network_options]
@@ -259,7 +260,7 @@ module VagrantPlugins
         # public network
         #
         # @param [Hash] network_options Docker scoped networking options
-        # @param [String] interface The bridge interface used
+        # @param [Socket::Ifaddr] interface The bridge interface used
         # @param [Hash] env Local call env
         # @return [String] Address range
         def request_public_iprange(network_options, interface, env)
@@ -273,7 +274,7 @@ module VagrantPlugins
           while !range
             range = env[:ui].ask(I18n.t(
               "docker_provider.network_bridge_iprange_request",
-              interface: interface,
+              interface: interface.name,
               default_range: network_options[:subnet]) + " ",
               prefix: false
             ).strip
@@ -283,10 +284,12 @@ module VagrantPlugins
             begin
               range = IPAddr.new(range)
               if !subnet.include?(range)
+                netmask = interface.netmask.ip_unpack.first
+                prefix = IPAddr.new("255.255.255.255/#{netmask}").to_i.to_s(2).count("1")
                 env[:ui].warn(I18n.t(
                   "docker_provider.network_bridge_iprange_outofbounds",
                   subnet: network_options[:subnet],
-                  range: "#{range}/#{range.prefix}"
+                  range: "#{range}/#{prefix}"
                 ) + "\n", prefix: false)
                 range = nil
               end
@@ -297,7 +300,9 @@ module VagrantPlugins
               range = nil
             end
           end
-          prefix = range.ipv4? ? 24 : 64
+
+          netmask = interface.netmask.ip_unpack.first
+          prefix = IPAddr.new("255.255.255.255/#{netmask}").to_i.to_s(2).count("1")
           "#{range}/#{prefix}"
         end
 
diff --git a/test/unit/plugins/providers/docker/action/prepare_networks_test.rb b/test/unit/plugins/providers/docker/action/prepare_networks_test.rb
index 039669417..17424b9a2 100644
--- a/test/unit/plugins/providers/docker/action/prepare_networks_test.rb
+++ b/test/unit/plugins/providers/docker/action/prepare_networks_test.rb
@@ -305,7 +305,8 @@ describe VagrantPlugins::DockerProvider::Action::PrepareNetworks do
 
   describe "#process_public_network" do
     let(:options) { {:ip=>"172.30.130.2", :subnet=>"172.30.0.0/16", :driver=>"bridge", :id=>"30e017d5-488f-5a2f-a3ke-k8dce8246b60"} }
-    let(:ipaddr) { double("ipaddr", prefix: 22, succ: "10.1.10.2", ipv4?: true, ipv6?: false) }
+    let(:ipaddr) { double("ipaddr", prefix: 22, succ: "10.1.10.2", ipv4?: true,
+                          ipv6?: false, to_i: 4294967040) }
 
     it "raises an error if there are no network interfaces" do
       expect(subject).to receive(:list_interfaces).and_return([])
@@ -351,13 +352,20 @@ describe VagrantPlugins::DockerProvider::Action::PrepareNetworks do
     let(:subnet) { double("ipaddr", to_s: "172.30.130.2", prefix: 22, succ: "172.30.130.3",
                           ipv6?: false) }
 
+    let(:ipaddr_prefix) { double("ipaddr_prefix", to_s: "255.255.255.255/255.255.255.0",
+                                 to_i: 4294967040 ) }
+
+    let(:netmask) { double("netmask", ip_unpack: ["255.255.255.0", 0]) }
+    let(:interface) { double("interface", name: "bridge", netmask: netmask) }
+
     it "requests a public ip range" do
       allow(IPAddr).to receive(:new).with(options[:subnet]).and_return(subnet)
       allow(IPAddr).to receive(:new).with("172.30.130.2").and_return(ipaddr)
+      allow(IPAddr).to receive(:new).with("255.255.255.255/255.255.255.0").and_return(ipaddr_prefix)
       allow(subnet).to receive(:include?).and_return(true)
       allow(machine.ui).to receive(:ask).and_return(options[:ip])
 
-      addr = subject.request_public_iprange(options, "bridge", env)
+      addr = subject.request_public_iprange(options, interface, env)
     end
   end
 end