diff --git a/lib/thor/parser/option.rb b/lib/thor/parser/option.rb
index 654f7adce..fa9bcf9b0 100644
--- a/lib/thor/parser/option.rb
+++ b/lib/thor/parser/option.rb
@@ -127,7 +127,8 @@ def validate_default_type!
         @default.class.name.downcase.to_sym
       end
 
-      raise ArgumentError, "An option's default must match its type." unless default_type == @type
+      # TODO: This should raise an ArgumentError in a future version of Thor
+      warn "Expected #{@type} default value for '#{switch_name}'; got #{@default.inspect} (#{default_type})" unless default_type == @type
     end
 
     def dasherized?
diff --git a/spec/parser/option_spec.rb b/spec/parser/option_spec.rb
index 8a7c329b4..7dca4fd6b 100644
--- a/spec/parser/option_spec.rb
+++ b/spec/parser/option_spec.rb
@@ -135,9 +135,9 @@ def option(name, options = {})
   end
 
   it "raises an error if default is inconsistent with type" do
-    expect do
-      option("foo", :type => :numeric, :default => "bar")
-    end.to raise_error(ArgumentError, "An option's default must match its type.")
+    expect(capture(:stderr) do
+      option("foo_bar", :type => :numeric, :default => "baz")
+    end.chomp).to eq('Expected numeric default value for \'--foo-bar\'; got "baz" (string)')
   end
 
   it "does not raises an error if default is an symbol and type string" do