diff --git a/mustermann/lib/mustermann/expander.rb b/mustermann/lib/mustermann/expander.rb
index fe8cc29..f9d5c1a 100644
--- a/mustermann/lib/mustermann/expander.rb
+++ b/mustermann/lib/mustermann/expander.rb
@@ -2,6 +2,7 @@
 require 'mustermann/ast/expander'
 require 'mustermann/caster'
 require 'mustermann'
+require 'addressable/uri'
 
 module Mustermann
   # Allows fine-grained control over pattern expansion.
@@ -194,8 +195,9 @@ def slice(hash, keys)
 
     def append(uri, values)
       return uri unless values and values.any?
-      entries = values.map { |pair| pair.map { |e| @api_expander.escape(e, also_escape: /[\/\?#\&\=%]/) }.join(?=) }
-      "#{ uri }#{ uri[??]??&:?? }#{ entries.join(?&) }"
+      Addressable::URI.encode(
+        [uri, uri.include?('?') ? '&' : '?', QueryStringBuilder.new(values).build].join
+      )
     end
 
     def map_values(values)
@@ -205,5 +207,45 @@ def map_values(values)
     end
 
     private :with_rest, :slice, :append, :caster, :map_values, :split_values
+
+    class QueryStringBuilder # :nodoc:
+      attr_reader :query
+
+      def initialize(query = {})
+        @query = query
+      end
+
+      def build
+        query.map { |key, value|
+          if value.is_a?(Array)
+            build_array_query(key, value)
+          elsif value.is_a?(Hash)
+            build_hash_query(key, value)
+          else
+            "#{key}=#{value}"
+          end
+        }.join('&')
+      end
+
+      private
+
+      def build_array_query(key, values)
+        query_key = "#{key}[]"
+        values.map { |v| [query_key, v].join('=') }.join('&')
+      end
+
+      def build_hash_query(key, values)
+        values.map { |h_key, h_value|
+          query_key = "#{key}[#{h_key}]"
+          if h_value.is_a?(Hash)
+            build_hash_query(query_key, h_value)
+          elsif h_value.is_a?(Array)
+            build_array_query(query_key, h_value)
+          else
+            [query_key, h_value].join('=')
+          end
+        }.join('&')
+      end
+    end
   end
 end
diff --git a/mustermann/spec/expander_spec.rb b/mustermann/spec/expander_spec.rb
index 342ed94..0748556 100644
--- a/mustermann/spec/expander_spec.rb
+++ b/mustermann/spec/expander_spec.rb
@@ -70,6 +70,9 @@
       subject(:expander) { Mustermann::Expander.new('/:a', additional_values: :append) }
       example { expander.expand(a: ?a).should be == '/a' }
       example { expander.expand(a: ?a, b: ?b).should be == '/a?b=b' }
+      example { expander.expand(a: ?a, b: [?b]).should be == '/a?b%5B%5D=b' }
+      example { expander.expand(a: ?a, b: {c: ?c}).should be == '/a?b%5Bc%5D=c' }
+      example { expander.expand(a: ?a, b: {c: [1, 2]}).should be == '/a?b%5Bc%5D%5B%5D=1&b%5Bc%5D%5B%5D=2' }
       example { expect { expander.expand(b: ?b) }.to raise_error(Mustermann::ExpandError) }
     end
   end