diff --git a/lib/mongoid/attributes/dynamic.rb b/lib/mongoid/attributes/dynamic.rb
index 294b418a0f..ad7ad71ef2 100644
--- a/lib/mongoid/attributes/dynamic.rb
+++ b/lib/mongoid/attributes/dynamic.rb
@@ -20,7 +20,7 @@ module Dynamic
       def respond_to?(name, include_private = false)
         super || (
           attributes &&
-          attributes.has_key?(name.to_s.reader)
+          attributes.has_key?(__dynamic_reader(name))
         )
       end
 
@@ -33,7 +33,7 @@ def respond_to?(name, include_private = false)
       #
       # @param [ String ] name The name of the field.
       def define_dynamic_reader(name)
-        return unless name.valid_method_name?
+        return unless valid_method_name?(name)
 
         class_eval do
           define_method(name) do
@@ -69,7 +69,7 @@ def define_dynamic_before_type_cast_reader(name)
       #
       # @param [ String ] name The name of the field.
       def define_dynamic_writer(name)
-        return unless name.valid_method_name?
+        return unless valid_method_name?(name)
 
         class_eval do
           define_method("#{name}=") do |value|
@@ -120,23 +120,53 @@ def inspect_dynamic_fields
       #
       # @return [ Object ] The result of the method call.
       def method_missing(name, *args)
-        attr = name.to_s
-        return super unless attributes.has_key?(attr.reader)
-        if attr.writer?
-          getter = attr.reader
-          define_dynamic_writer(getter)
-          write_attribute(getter, args.first)
-        elsif attr.before_type_cast?
-          define_dynamic_before_type_cast_reader(attr.reader)
-          attribute_will_change!(attr.reader)
-          read_attribute_before_type_cast(attr.reader)
+        reader = __dynamic_reader(name)
+        return super unless attributes.has_key?(reader)
+        if __dynamic_writer?(name)
+          define_dynamic_writer(reader)
+          write_attribute(reader, args.first)
+        elsif name.to_s.ends_with?('_before_type_cast')
+          define_dynamic_before_type_cast_reader(reader)
+          attribute_will_change!(reader)
+          read_attribute_before_type_cast(reader)
         else
-          getter = attr.reader
-          define_dynamic_reader(getter)
-          attribute_will_change!(attr.reader)
-          read_raw_attribute(getter)
+          define_dynamic_reader(reader)
+          attribute_will_change!(reader)
+          read_raw_attribute(reader)
         end
       end
+
+      private
+
+      # Get the string as a getter string.
+      #
+      # @example Get the reader/getter
+      #   "model=".reader
+      #
+      # @return [ String ] The string stripped of "=".
+      def __dynamic_reader(method)
+        method.to_s.delete("=").sub(/_before_type_cast\z/, '')
+      end
+
+      # Is this string a writer?
+      #
+      # @example Is the string a setter method?
+      #   "model=".writer?
+      #
+      # @return [ true | false ] If the string contains "=".
+      def __dynamic_writer?(method)
+        method.to_s.include?("=")
+      end
+
+      # Is this string a valid_method_name?
+      #
+      # @example Is the string a valid Ruby identifier for use as a method name
+      #   "model=".valid_method_name?
+      #
+      # @return [ true | false ] If the string contains a valid Ruby identifier.
+      def valid_method_name?(method)
+        !method.to_s.match?(/[@$"-]/)
+      end
     end
   end
 end
diff --git a/lib/mongoid/extensions/string.rb b/lib/mongoid/extensions/string.rb
index b541b3adc9..783c37b995 100644
--- a/lib/mongoid/extensions/string.rb
+++ b/lib/mongoid/extensions/string.rb
@@ -88,47 +88,6 @@ def numeric?
         (self =~ /\A(?:NaN|-?Infinity)\z/) == 0
       end
 
-      # Get the string as a getter string.
-      #
-      # @example Get the reader/getter
-      #   "model=".reader
-      #
-      # @return [ String ] The string stripped of "=".
-      def reader
-        delete("=").sub(/\_before\_type\_cast\z/, '')
-      end
-
-      # Is this string a writer?
-      #
-      # @example Is the string a setter method?
-      #   "model=".writer?
-      #
-      # @return [ true | false ] If the string contains "=".
-      def writer?
-        include?("=")
-      end
-
-      # Is this string a valid_method_name?
-      #
-      # @example Is the string a valid Ruby identifier for use as a method name
-      #   "model=".valid_method_name?
-      #
-      # @return [ true | false ] If the string contains a valid Ruby identifier.
-      def valid_method_name?
-        /[@$"-]/ !~ self
-      end
-
-      # Does the string end with _before_type_cast?
-      #
-      # @example Is the string a setter method?
-      #   "price_before_type_cast".before_type_cast?
-      #
-      # @return [ true | false ] If the string ends with "_before_type_cast"
-      def before_type_cast?
-        ends_with?("_before_type_cast")
-      end
-
-
       # Is the object not to be converted to bson on criteria creation?
       #
       # @example Is the object unconvertable?
diff --git a/spec/mongoid/attributes/dynamic_spec.rb b/spec/mongoid/attributes/dynamic_spec.rb
index 8dff0e1b3d..82e605ed42 100644
--- a/spec/mongoid/attributes/dynamic_spec.rb
+++ b/spec/mongoid/attributes/dynamic_spec.rb
@@ -150,4 +150,62 @@
 
     it_behaves_like 'dynamic field'
   end
+
+  describe "#reader" do
+
+    context "when string is a reader" do
+
+      it "returns self" do
+        expect("attribute".reader).to eq("attribute")
+      end
+    end
+
+    context "when string is a writer" do
+
+      it "returns the reader" do
+        expect("attribute=".reader).to eq("attribute")
+      end
+    end
+
+    context "when the string is before_type_cast" do
+
+      it "returns the reader" do
+        expect("attribute_before_type_cast".reader).to eq("attribute")
+      end
+    end
+  end
+
+  describe "#writer?" do
+
+    context "when string is a reader" do
+
+      it "returns false" do
+        expect("attribute".writer?).to be false
+      end
+    end
+
+    context "when string is a writer" do
+
+      it "returns true" do
+        expect("attribute=".writer?).to be true
+      end
+    end
+  end
+
+  describe "#before_type_cast?" do
+
+    context "when string is a reader" do
+
+      it "returns false" do
+        expect("attribute".before_type_cast?).to be false
+      end
+    end
+
+    context "when string is before_type_cast" do
+
+      it "returns true" do
+        expect("attribute_before_type_cast".before_type_cast?).to be true
+      end
+    end
+  end
 end
diff --git a/spec/mongoid/extensions/string_spec.rb b/spec/mongoid/extensions/string_spec.rb
index 5f057ad17a..89c5de2a4f 100644
--- a/spec/mongoid/extensions/string_spec.rb
+++ b/spec/mongoid/extensions/string_spec.rb
@@ -199,30 +199,6 @@ class Patient
     end
   end
 
-  describe "#reader" do
-
-    context "when string is a reader" do
-
-      it "returns self" do
-        expect("attribute".reader).to eq("attribute")
-      end
-    end
-
-    context "when string is a writer" do
-
-      it "returns the reader" do
-        expect("attribute=".reader).to eq("attribute")
-      end
-    end
-
-    context "when the string is before_type_cast" do
-
-      it "returns the reader" do
-        expect("attribute_before_type_cast".reader).to eq("attribute")
-      end
-    end
-  end
-
   describe "#numeric?" do
 
     context "when the string is an integer" do
@@ -319,39 +295,4 @@ class Patient
       end
     end
   end
-
-  describe "#writer?" do
-
-    context "when string is a reader" do
-
-      it "returns false" do
-        expect("attribute".writer?).to be false
-      end
-    end
-
-    context "when string is a writer" do
-
-      it "returns true" do
-        expect("attribute=".writer?).to be true
-      end
-    end
-  end
-
-  describe "#before_type_cast?" do
-
-    context "when string is a reader" do
-
-      it "returns false" do
-        expect("attribute".before_type_cast?).to be false
-      end
-    end
-
-    context "when string is before_type_cast" do
-
-      it "returns true" do
-        expect("attribute_before_type_cast".before_type_cast?).to be true
-      end
-    end
-  end
-
 end