diff --git a/lib/mrsk/configuration.rb b/lib/mrsk/configuration.rb
index f95de700..074c7cf3 100644
--- a/lib/mrsk/configuration.rb
+++ b/lib/mrsk/configuration.rb
@@ -80,7 +80,7 @@ class Mrsk::Configuration
   end
 
   def primary_web_host
-    role(:web).hosts.first
+    role(:web).primary_host
   end
 
   def traefik_hosts
@@ -196,6 +196,12 @@ class Mrsk::Configuration
         raise ArgumentError, "You must specify a password for the registry in config/deploy.yml (or set the ENV variable if that's used)"
       end
 
+      roles.each do |role|
+        if role.hosts.empty?
+          raise ArgumentError, "No servers specified for the #{role.name} role"
+        end
+      end
+
       true
     end
 
diff --git a/lib/mrsk/configuration/role.rb b/lib/mrsk/configuration/role.rb
index f3e20e9a..bfc42fbe 100644
--- a/lib/mrsk/configuration/role.rb
+++ b/lib/mrsk/configuration/role.rb
@@ -7,6 +7,10 @@ class Mrsk::Configuration::Role
    @name, @config = name.inquiry, config
   end
 
+  def primary_host
+    hosts.first
+  end
+
   def hosts
     @hosts ||= extract_hosts_from_config
   end
@@ -55,7 +59,7 @@ class Mrsk::Configuration::Role
         config.servers
       else
         servers = config.servers[name]
-        servers.is_a?(Array) ? servers : servers["hosts"]
+        servers.is_a?(Array) ? servers : Array(servers["hosts"])
       end
     end
 
diff --git a/test/configuration_test.rb b/test/configuration_test.rb
index 30c4b049..ee381449 100644
--- a/test/configuration_test.rb
+++ b/test/configuration_test.rb
@@ -26,14 +26,19 @@ class ConfigurationTest < ActiveSupport::TestCase
     ENV.delete("VERSION")
   end
 
-  test "ensure valid keys" do
-    assert_raise(ArgumentError) do
-      Mrsk::Configuration.new(@deploy.tap { _1.delete(:service) })
-      Mrsk::Configuration.new(@deploy.tap { _1.delete(:image) })
-      Mrsk::Configuration.new(@deploy.tap { _1.delete(:registry) })
+  %i[ service image registry ].each do |key|
+    test "#{key} config required" do
+      assert_raise(ArgumentError) do
+        Mrsk::Configuration.new @deploy.tap { _1.delete key }
+      end
+    end
+  end
 
-      Mrsk::Configuration.new(@deploy.tap { _1[:registry].delete("username") })
-      Mrsk::Configuration.new(@deploy.tap { _1[:registry].delete("password") })
+  %w[ username password ].each do |key|
+    test "registry #{key} required" do
+      assert_raise(ArgumentError) do
+        Mrsk::Configuration.new @deploy.tap { _1[:registry].delete key }
+      end
     end
   end
 
@@ -148,6 +153,39 @@ class ConfigurationTest < ActiveSupport::TestCase
 
   test "valid config" do
     assert @config.valid?
+    assert @config_with_roles.valid?
+  end
+
+  test "hosts required for all roles" do
+    # Empty server list for implied web role
+    assert_raises(ArgumentError) do
+      Mrsk::Configuration.new @deploy.merge(servers: [])
+    end
+
+    # Empty server list
+    assert_raises(ArgumentError) do
+      Mrsk::Configuration.new @deploy.merge(servers: { "web" => [] })
+    end
+
+    # Missing hosts key
+    assert_raises(ArgumentError) do
+      Mrsk::Configuration.new @deploy.merge(servers: { "web" => {} })
+    end
+
+    # Empty hosts list
+    assert_raises(ArgumentError) do
+      Mrsk::Configuration.new @deploy.merge(servers: { "web" => { "hosts" => [] } })
+    end
+
+    # Nil hosts
+    assert_raises(ArgumentError) do
+      Mrsk::Configuration.new @deploy.merge(servers: { "web" => { "hosts" => nil } })
+    end
+
+    # One role with hosts, one without
+    assert_raises(ArgumentError) do
+      Mrsk::Configuration.new @deploy.merge(servers: { "web" => %w[ web ], "workers" => { "hosts" => %w[ ] } })
+    end
   end
 
   test "ssh options" do