diff --git a/lib/rails_erd/cli.rb b/lib/rails_erd/cli.rb
index a1de4e3..ea0d94f 100644
--- a/lib/rails_erd/cli.rb
+++ b/lib/rails_erd/cli.rb
@@ -8,6 +8,7 @@
   option :generator do
     long "--generator=Generator"
     desc "Generator to use (graphviz or mermaid). Defaults to graphviz."
+    default "graphviz"
   end
 
   option :title do
@@ -164,7 +165,8 @@ def start
 
     def initialize(path, options)
       @path, @options = path, options
-      require "rails_erd/diagram/graphviz" if options.generator == :graphviz
+      require "rails_erd/diagram/graphviz" if options[:generator] == 'graphviz'
+      require "rails_erd/diagram/mermaid" if options[:generator] == 'mermaid'
     end
 
     def start
@@ -202,7 +204,7 @@ def load_application
     end
 
     def generator
-      if options.generator == :mermaid
+      if options[:generator] == 'mermaid'
         RailsERD::Diagram::Mermaid
       else
         RailsERD::Diagram::Graphviz