diff --git a/lib/fast_blank.rb b/lib/fast_blank.rb
index cf370a6..39fdced 100644
--- a/lib/fast_blank.rb
+++ b/lib/fast_blank.rb
@@ -1,3 +1,8 @@
+class ::String
+  # Explicitly undefine method before redefining to avoid Ruby warnings.
+  undef_method(:blank?) if method_defined?(:blank?)
+end
+
 case RUBY_ENGINE
   when 'jruby'
     require 'fast_blank.jar'
diff --git a/spec/fast_blank_spec.rb b/spec/fast_blank_spec.rb
index bed89e9..4317b0f 100644
--- a/spec/fast_blank_spec.rb
+++ b/spec/fast_blank_spec.rb
@@ -1,11 +1,18 @@
-require 'fast_blank'
+$VERBOSE = true
 
 class ::String
+  # Stub the original method to make sure it is redefined correctly.
+  def blank?
+    raise NotImplementedError
+  end
+
   def blank2?
     /\A[[:space:]]*\z/ === self
   end
 end
 
+require 'fast_blank'
+
 describe String do
   it "works" do
     expect("".blank?).to eq(true)