diff --git a/lib/jekyll/drops/collection_drop.rb b/lib/jekyll/drops/collection_drop.rb
index ccb3045a..009635a4 100644
--- a/lib/jekyll/drops/collection_drop.rb
+++ b/lib/jekyll/drops/collection_drop.rb
@@ -1,11 +1,13 @@
 # encoding: UTF-8
-require "jekyll/drops/immutable_drop"
+require "jekyll/drops/drop"
 
 module Jekyll
   module Drops
-    class CollectionDrop < ImmutableDrop
+    class CollectionDrop < Drop
       extend Forwardable
 
+      mutable false
+
       def_delegator :@obj, :write?, :output
       def_delegators :@obj, :label, :docs, :files, :directory,
                             :relative_directory
diff --git a/lib/jekyll/drops/document_drop.rb b/lib/jekyll/drops/document_drop.rb
index 81c9bcd2..f6e03fec 100644
--- a/lib/jekyll/drops/document_drop.rb
+++ b/lib/jekyll/drops/document_drop.rb
@@ -2,9 +2,11 @@
 
 module Jekyll
   module Drops
-    class DocumentDrop < ImmutableDrop
+    class DocumentDrop < Drop
       extend Forwardable
 
+      mutable false
+
       def_delegator :@obj, :next_doc, :next
       def_delegator :@obj, :previous_doc, :previous
       def_delegator :@obj, :relative_path, :path
diff --git a/lib/jekyll/drops/drop.rb b/lib/jekyll/drops/drop.rb
new file mode 100644
index 00000000..09bdb2d2
--- /dev/null
+++ b/lib/jekyll/drops/drop.rb
@@ -0,0 +1,74 @@
+# encoding: UTF-8
+
+module Jekyll
+  module Drops
+    class Drop < Liquid::Drop
+      # Get or set whether the drop class is mutable.
+      # Mutability determines whether or not pre-defined fields may be
+      # overwritten.
+      #
+      # is_mutable - Boolean set mutability of the class (default: nil)
+      #
+      # Returns the mutability of the class
+      def self.mutable(is_mutable = nil)
+        if is_mutable
+          @is_mutable = is_mutable
+        end
+        @is_mutable || false
+      end
+
+      # Create a new Drop
+      #
+      # obj - the Jekyll Site, Collection, or Document required by the
+      # drop.
+      #
+      # Returns nothing
+      def initialize(obj)
+        @obj = obj
+        @mutations = {} # only if mutable: true
+      end
+
+      # Access a method in the Drop or a field in the underlying hash data.
+      # If mutable, checks the mutations first. Then checks the methods,
+      # and finally check the underlying hash (e.g. document front matter)
+      # if all the previous places didn't match.
+      #
+      # key - the string key whose value to fetch
+      #
+      # Returns the value for the given key, or nil if none exists
+      def [](key)
+        if self.class.mutable && @mutations.key?(key)
+          @mutations[key]
+        elsif respond_to? key
+          public_send key
+        else
+          fallback_data[key]
+        end
+      end
+
+      # Set a field in the Drop. If mutable, sets in the mutations and
+      # returns. If not mutable, checks first if it's trying to override a
+      # Drop method and raises a DropMutationException if so. If not
+      # mutable and the key is not a method on the Drop, then it sets the
+      # key to the value in the underlying hash (e.g. document front
+      # matter)
+      #
+      # key - the String key whose value to set
+      # val - the Object to set the key's value to
+      #
+      # Returns the value the key was set to unless the Drop is not mutable
+      # and the key matches a method in which case it raises a
+      # DropMutationException.
+      def []=(key, val)
+        if self.class.mutable
+          @mutations[key] = val
+        elsif respond_to? key
+          raise Errors::DropMutationException, "Key #{key} cannot be set in the drop."
+        else
+          fallback_data[key] = val
+        end
+      end
+
+    end
+  end
+end
diff --git a/lib/jekyll/drops/immutable_drop.rb b/lib/jekyll/drops/immutable_drop.rb
deleted file mode 100644
index 5440aa00..00000000
--- a/lib/jekyll/drops/immutable_drop.rb
+++ /dev/null
@@ -1,28 +0,0 @@
-# encoding: UTF-8
-
-module Jekyll
-  module Drops
-    class ImmutableDrop < Liquid::Drop
-      def initialize(obj)
-        @obj = obj
-      end
-
-      def [](key)
-        if respond_to? key
-          public_send key
-        else
-          fallback_data[key]
-        end
-      end
-
-      def []=(key, val)
-        if respond_to? key
-          raise DropMutationException, "Key #{key} cannot be set in the drop."
-        else
-          fallback_data[key] = val
-        end
-      end
-
-    end
-  end
-end
diff --git a/lib/jekyll/drops/mutable_drop.rb b/lib/jekyll/drops/mutable_drop.rb
deleted file mode 100644
index 9dd4048d..00000000
--- a/lib/jekyll/drops/mutable_drop.rb
+++ /dev/null
@@ -1,28 +0,0 @@
-# encoding: UTF-8
-
-module Jekyll
-  module Drops
-    class MutableDrop < Liquid::Drop
-
-      def initialize(obj)
-        @obj = obj
-        @mutations = {}
-      end
-
-      def [](key)
-        if @mutations.key? key
-          @mutations[key]
-        elsif respond_to? key
-          public_send key
-        else
-          fallback_data[key]
-        end
-      end
-
-      def []=(key, val)
-        @mutations[key] = val
-      end
-
-    end
-  end
-end
diff --git a/lib/jekyll/drops/site_drop.rb b/lib/jekyll/drops/site_drop.rb
index 61ac8098..ec4f0910 100644
--- a/lib/jekyll/drops/site_drop.rb
+++ b/lib/jekyll/drops/site_drop.rb
@@ -2,9 +2,11 @@
 
 module Jekyll
   module Drops
-    class SiteDrop < ImmutableDrop
+    class SiteDrop < Drop
       extend Forwardable
 
+      mutable false
+
       def_delegator  :@obj, :site_data, :data
       def_delegators :@obj, :time, :pages, :static_files, :documents,
                             :tags, :categories
diff --git a/lib/jekyll/drops/unified_payload_drop.rb b/lib/jekyll/drops/unified_payload_drop.rb
index 6db48f66..3c593ba6 100644
--- a/lib/jekyll/drops/unified_payload_drop.rb
+++ b/lib/jekyll/drops/unified_payload_drop.rb
@@ -2,7 +2,8 @@
 
 module Jekyll
   module Drops
-    class UnifiedPayloadDrop < ImmutableDrop
+    class UnifiedPayloadDrop < Drop
+      mutable false
 
       attr_accessor :page, :layout, :content, :paginator
       attr_accessor :highlighter_prefix, :highlighter_suffix
diff --git a/lib/jekyll/drops/url_drop.rb b/lib/jekyll/drops/url_drop.rb
index 163591dd..a2bf6262 100644
--- a/lib/jekyll/drops/url_drop.rb
+++ b/lib/jekyll/drops/url_drop.rb
@@ -2,9 +2,11 @@
 
 module Jekyll
   module Drops
-    class UrlDrop < ImmutableDrop
+    class UrlDrop < Drop
       extend Forwardable
 
+      mutable false
+
       def_delegator :@obj, :cleaned_relative_path, :path
       def_delegator :@obj, :output_ext, :output_ext