diff --git a/spec/std/yaml/mapping_spec.cr b/spec/std/yaml/mapping_spec.cr
index 2bee92530218..81108679eadd 100644
--- a/spec/std/yaml/mapping_spec.cr
+++ b/spec/std/yaml/mapping_spec.cr
@@ -20,6 +20,13 @@ private class StrictYAMLPerson
   }, true)
 end
 
+private class YAMLPersonWithExtras
+  YAML.mapping({
+    name: {type: String},
+    age:  {type: Int32, nilable: true},
+  }, extra: "extras")
+end
+
 private class YAMLWithBool
   YAML.mapping value: Bool
 end
@@ -145,6 +152,15 @@ describe "YAML mapping" do
     end
     ex.location.should eq({3, 1})
   end
+  it "parses person with extra attributes" do
+    person = YAMLPersonWithExtras.from_yaml("---\nname: John\nunknown: [1, 2, 3]\nage: 30\n")
+    person.should be_a(YAMLPersonWithExtras)
+    person.name.should eq("John")
+    person.age.should eq(30)
+    person.extras.should be_a(Hash(String, YAML::Any))
+    person.extras["unknown"].should be_a(YAML::Any)
+    person.extras["unknown"].size.should eq(3)
+  end
 
   it "does to_yaml" do
     person = YAMLPerson.from_yaml("---\nname: John\nage: 30\n")
diff --git a/src/json/mapping.cr b/src/json/mapping.cr
index 68353789f8a2..a85c288b592f 100644
--- a/src/json/mapping.cr
+++ b/src/json/mapping.cr
@@ -60,7 +60,11 @@ module JSON
   # If *strict* is `true`, unknown properties in the JSON
   # document will raise a parse exception. The default is `false`, so unknown properties
   # are silently ignored.
-  macro mapping(properties, strict = false)
+  macro mapping(properties, strict = false, extra = nil)
+    {% if extra && properties.keys.includes? extra.id %}
+      {{ raise "Name for extra property already in use: #{extra.id}" }}
+    {% end %}
+
     {% for key, value in properties %}
       {% properties[key] = {type: value} unless value.is_a?(HashLiteral) || value.is_a?(NamedTupleLiteral) %}
     {% end %}
@@ -89,12 +93,24 @@ module JSON
       {% end %}
     {% end %}
 
+    {% if extra %}
+      @{{extra.id}} : Hash(String, ::JSON::Any)
+
+      def {{extra.id}}
+        @{{extra.id}}
+      end
+    {% end %}
+
     def initialize(%pull : ::JSON::PullParser)
       {% for key, value in properties %}
         %var{key.id} = nil
         %found{key.id} = false
       {% end %}
 
+      {% if extra %}
+        @{{extra.id}} = Hash(String, ::JSON::Any).new
+      {% end %}
+
       %location = %pull.location
       %pull.read_begin_object
       while %pull.kind != :end_object
@@ -130,6 +146,8 @@ module JSON
         else
           {% if strict %}
             raise ::JSON::ParseException.new("Unknown json attribute: #{key}", *%key_location)
+          {% elsif extra %}
+            @{{extra.id}}[key] = ::JSON::Any.new(%pull)
           {% else %}
             %pull.skip
           {% end %}
diff --git a/src/yaml/mapping.cr b/src/yaml/mapping.cr
index f02d0ebff1a0..f813aaf64932 100644
--- a/src/yaml/mapping.cr
+++ b/src/yaml/mapping.cr
@@ -67,7 +67,11 @@ module YAML
   # it and initializes this type's instance variables.
   #
   # This macro also declares instance variables of the types given in the mapping.
-  macro mapping(properties, strict = false)
+  macro mapping(properties, strict = false, extra = nil)
+    {% if extra && properties.keys.includes? extra.id %}
+      {{ raise "Name for extra property already in use: #{extra.id}" }}
+    {% end %}
+
     {% for key, value in properties %}
       {% properties[key] = {type: value} unless value.is_a?(HashLiteral) || value.is_a?(NamedTupleLiteral) %}
     {% end %}
@@ -96,12 +100,24 @@ module YAML
       {% end %}
     {% end %}
 
+    {% if extra %}
+      @{{extra.id}} : Hash(String, ::YAML::Any)
+
+      def {{extra.id}}
+        @{{extra.id}}
+      end
+    {% end %}
+
     def initialize(%pull : ::YAML::PullParser)
       {% for key, value in properties %}
         %var{key.id} = nil
         %found{key.id} = false
       {% end %}
 
+      {% if extra %}
+        @{{extra.id}} = Hash(String, ::YAML::Any).new
+      {% end %}
+
       %mapping_location = %pull.location
 
       %pull.read_mapping_start
@@ -129,6 +145,8 @@ module YAML
         else
           {% if strict %}
             raise ::YAML::ParseException.new("Unknown yaml attribute: #{key}", *%key_location)
+          {% elsif extra %}
+            @{{extra.id}}[key] = ::YAML::Any.new(%pull)
           {% else %}
             %pull.skip
           {% end %}
@@ -182,6 +200,14 @@ module YAML
             {% end %}
           end
         {% end %}
+        {% if extra %}
+          _{{extra.id}} = @{{extra.id}}
+
+          unless _{{extra.id}}.nil?
+            "{{extra.id}}".to_yaml(%yaml)
+            _{{extra.id}}.to_yaml(%yaml)
+          end
+        {% end %}
       end
     end
   end