diff --git a/lib/rspec/parameterized/core.rb b/lib/rspec/parameterized/core.rb
index ad3aa38..09ad249 100644
--- a/lib/rspec/parameterized/core.rb
+++ b/lib/rspec/parameterized/core.rb
@@ -1,10 +1,14 @@
 require "rspec/parameterized/core/version"
 require 'parser'
 require 'unparser'
-require 'proc_to_ast'
 require 'rspec/parameterized/core/helper_methods'
 require 'rspec/parameterized/core/example_helper_methods'
 
+begin
+  require 'proc_to_ast'
+rescue LoadError
+end
+
 module RSpec
   module Parameterized
     module Core
@@ -144,7 +148,7 @@ def define_cases(parameter, *args, &block)
 
         def params_inspect(obj)
           begin
-            obj.is_a?(Proc) ? obj.to_raw_source : obj.inspect
+            obj.is_a?(Proc) && obj.respond_to?(:to_raw_source) ? obj.to_raw_source : obj.inspect
           rescue Parser::SyntaxError
             return obj.inspect
           end
diff --git a/lib/rspec/parameterized/core/lazy_arg.rb b/lib/rspec/parameterized/core/lazy_arg.rb
index 5d77e70..e8e0fe4 100644
--- a/lib/rspec/parameterized/core/lazy_arg.rb
+++ b/lib/rspec/parameterized/core/lazy_arg.rb
@@ -11,6 +11,8 @@ def apply(obj)
         end
 
         def inspect
+          return super.inspect unless @block.respond_to?(:to_raw_source)
+
           "#{@block.to_raw_source}"
         rescue Parser::SyntaxError
           super.inspect
diff --git a/rspec-parameterized-core.gemspec b/rspec-parameterized-core.gemspec
index 1b40131..70c373b 100644
--- a/rspec-parameterized-core.gemspec
+++ b/rspec-parameterized-core.gemspec
@@ -33,10 +33,10 @@ I was inspired by [udzura's mock](https://gist.github.com/1881139).}
   spec.require_paths = ["lib"]
 
   spec.add_dependency "parser"
-  spec.add_dependency "proc_to_ast", ">= 0.2.0"
   spec.add_dependency "rspec", ">= 2.13", "< 4"
   spec.add_dependency "unparser"
 
+  spec.add_development_dependency "proc_to_ast", ">= 0.2.0"
   spec.add_development_dependency "rake", ">= 12.0.0"
 
   # For more information and examples about making a new gem, check out our
diff --git a/spec/rspec/parameterized/core_spec.rb b/spec/rspec/parameterized/core_spec.rb
index fbc966b..b84d304 100644
--- a/spec/rspec/parameterized/core_spec.rb
+++ b/spec/rspec/parameterized/core_spec.rb
@@ -326,7 +326,7 @@
     end
   end
 
-  context "when the where block is between with_thems" do
+  context "when the where block is between with_them" do
     with_them do
       it "should do additions" do
         expect(a + b).to eq answer