diff --git a/lib/jekyll/drops/drop.rb b/lib/jekyll/drops/drop.rb
index 09623ef9..600e68a0 100644
--- a/lib/jekyll/drops/drop.rb
+++ b/lib/jekyll/drops/drop.rb
@@ -55,6 +55,7 @@ module Jekyll
           fallback_data[key]
         end
       end
+      alias_method :invoke_drop, :[]
 
       # 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
@@ -103,7 +104,7 @@ module Jekyll
       #
       # Returns true if the given key is present
       def key?(key)
-        if self.class.mutable
+        if self.class.mutable?
           @mutations.key?(key)
         else
           !key.nil? && (respond_to?(key) || fallback_data.key?(key))
diff --git a/test/test_drop.rb b/test/test_drop.rb
index eb23feb0..7bcd3971 100644
--- a/test/test_drop.rb
+++ b/test/test_drop.rb
@@ -2,6 +2,18 @@
 
 require "helper"
 
+class DropFixture < Jekyll::Drops::Drop
+  mutable true
+
+  def foo
+    "bar"
+  end
+
+  def fallback_data
+    @fallback_data ||= {}
+  end
+end
+
 class TestDrop < JekyllUnitTest
   context "a document drop" do
     setup do
@@ -12,37 +24,67 @@ class TestDrop < JekyllUnitTest
       @document = @site.collections["methods"].docs.detect do |d|
         d.relative_path == "_methods/configuration.md"
       end
-      @drop = @document.to_liquid
+      @document_drop = @document.to_liquid
+      @drop = DropFixture.new({})
     end
 
     should "reject 'nil' key" do
       refute @drop.key?(nil)
     end
 
-    should "raise KeyError if key is not found and no default provided" do
-      assert_raises KeyError do
-        @drop.fetch("not_existing_key")
+    should "return values for #[]" do
+      assert_equal "bar", @drop["foo"]
+    end
+
+    should "return values for #invoke_drop" do
+      assert_equal "bar", @drop.invoke_drop("foo")
+    end
+
+    context "mutations" do
+      should "return mutations for #[]" do
+        @drop["foo"] = "baz"
+        assert_equal "baz", @drop["foo"]
+      end
+
+      should "return mutations for #invoke_drop" do
+        @drop["foo"] = "baz"
+        assert_equal "baz", @drop.invoke_drop("foo")
       end
     end
 
-    should "fetch value without default" do
-      assert_equal "Jekyll.configuration", @drop.fetch("title")
-    end
+    context "fetch" do
+      should "raise KeyError if key is not found and no default provided" do
+        assert_raises KeyError do
+          @document_drop.fetch("not_existing_key")
+        end
+      end
 
-    should "fetch default if key is not found" do
-      assert_equal "default", @drop.fetch("not_existing_key", "default")
-    end
+      should "fetch value without default" do
+        assert_equal "Jekyll.configuration", @document_drop.fetch("title")
+      end
 
-    should "fetch default boolean value correctly" do
-      assert_equal false, @drop.fetch("bar", false)
-    end
+      should "fetch default if key is not found" do
+        assert_equal "default", @document_drop.fetch("not_existing_key", "default")
+      end
 
-    should "fetch default value from block if key is not found" do
-      assert_equal "default bar", @drop.fetch("bar") { |el| "default #{el}" }
-    end
+      should "fetch default boolean value correctly" do
+        assert_equal false, @document_drop.fetch("bar", false)
+      end
 
-    should "fetch default value from block first if both argument and block given" do
-      assert_equal "baz", @drop.fetch("bar", "default") { "baz" }
+      should "fetch default value from block if key is not found" do
+        assert_equal "default bar", @document_drop.fetch("bar") { |el| "default #{el}" }
+      end
+
+      should "fetch default value from block first if both argument and block given" do
+        assert_equal "baz", @document_drop.fetch("bar", "default") { "baz" }
+      end
+
+      should "not change mutability when fetching" do
+        assert @drop.class.mutable?
+        @drop["foo"] = "baz"
+        assert_equal "baz", @drop.fetch("foo")
+        assert @drop.class.mutable?
+      end
     end
   end
 end