diff --git a/.travis.yml b/.travis.yml
index 488b19d..56da410 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,3 +1,8 @@
 language: crystal
 crystal:
   - latest
+  - nightly
+script:
+  - crystal spec
+  - crystal run examples/test.cr
+  - crystal run examples/test2.cr
diff --git a/examples/test.cr b/examples/test.cr
index 5be62fc..94deca1 100644
--- a/examples/test.cr
+++ b/examples/test.cr
@@ -23,9 +23,15 @@ puts Faker::Address.longitude
 puts "\n### Faker::Commerce\n\n"
 
 puts Faker::Commerce.color
+puts Faker::Commerce.unique_color
 puts Faker::Commerce.department
+puts Faker::Commerce.unique_department
+puts Faker::Commerce.unique_department(2)
+puts Faker::Commerce.unique_department(2, true)
 puts Faker::Commerce.product_name
 puts Faker::Commerce.price
+puts Faker::Commerce.unique_price
+puts Faker::Commerce.unique_price(0.0..10_000.00)
 
 puts "\n### Faker::Company\n\n"
 
@@ -38,10 +44,16 @@ puts "\n\t### Faker::Internet\n\n"
 
 puts Faker::Internet.email
 puts Faker::Internet.email("Nancy")
+puts Faker::Internet.unique_email("Nancy")
+puts Faker::Internet.unique_email("Nancy")
 puts Faker::Internet.free_email
+puts Faker::Internet.unique_free_email
 puts Faker::Internet.free_email("Nancy")
+puts Faker::Internet.unique_free_email("Nancy")
 puts Faker::Internet.safe_email
+puts Faker::Internet.unique_safe_email
 puts Faker::Internet.safe_email("Nancy")
+puts Faker::Internet.unique_safe_email("Nancy")
 
 puts Faker::Internet.user_name
 puts Faker::Internet.user_name("Nancy")
@@ -88,12 +100,25 @@ puts Faker::Name.prefix
 puts Faker::Name.suffix
 puts Faker::Name.title
 
+puts "\n\t### Faker::Avatar\n\n"
+
+puts Faker::Avatar.image
+puts Faker::Avatar.image("borp")
+puts Faker::Avatar.unique_image("borp")
+puts Faker::Avatar.unique_image("borp")
+
 puts "\n\t### Faker::Number\n\n"
 
 puts Faker::Number.number(10)
+# puts Faker::Number.unique_number(10)
+# puts Faker::Number.unique_number(10)
+# puts Faker::Number.unique_number(10)
 puts Faker::Number.decimal(2)
 puts Faker::Number.decimal(2, 3)
+puts Faker::Number.unique_decimal(2)
+# puts Faker::Number.unique_decimal(2, 3)
 puts Faker::Number.digit
+puts Faker::Number.unique_digit
 
 puts "\n\t### Faker::PhoneNumber\n\n"
 
@@ -101,6 +126,10 @@ puts Faker::PhoneNumber.phone_number
 
 puts "\n\t### Faker::Business\n\n"
 
-p Faker::Business.credit_card_number
-p Faker::Business.credit_card_expiry_date
-p Faker::Business.credit_card_type
+puts Faker::Business.credit_card_number
+puts Faker::Business.credit_card_expiry_date
+puts Faker::Business.credit_card_type
+
+puts Faker::Business.unique_credit_card_number
+puts Faker::Business.unique_credit_card_expiry_date
+puts Faker::Business.unique_credit_card_type
diff --git a/spec/address_spec.cr b/spec/address_spec.cr
index 876f4eb..046462b 100644
--- a/spec/address_spec.cr
+++ b/spec/address_spec.cr
@@ -21,4 +21,15 @@ describe Faker::Address do
     Faker::Address.latitude.should eq "-23.850993082533705"
     Faker::Address.longitude.should eq "-4.488135572134695"
   end
+
+  it "should generate unique result" do
+    Faker.seed 123456
+    vals = Array(String).new
+
+    10_000.times do |t|
+      vals << Faker::Address.unique_city
+    end
+
+    vals.size.should eq vals.uniq.size
+  end
 end
diff --git a/spec/internet_spec.cr b/spec/internet_spec.cr
index 83ae3b1..72f1db6 100644
--- a/spec/internet_spec.cr
+++ b/spec/internet_spec.cr
@@ -70,7 +70,7 @@ describe Faker::Internet do
   it "password_max_with_integer_arg" do
     (1..32).to_a.each do |min_length|
       max_length = min_length + 4
-        (Faker::Internet.password(min_length, max_length).size <= max_length).should be_true
+      (Faker::Internet.password(min_length, max_length).size <= max_length).should be_true
     end
   end
 
diff --git a/src/faker.cr b/src/faker.cr
index 8fb0d16..af31f12 100644
--- a/src/faker.cr
+++ b/src/faker.cr
@@ -1,4 +1,5 @@
 require "./data.cr"
+require "./faker/base"
 require "./faker/*"
 
 module Faker
diff --git a/src/faker/address.cr b/src/faker/address.cr
index 9a9720d..934133f 100644
--- a/src/faker/address.cr
+++ b/src/faker/address.cr
@@ -1,19 +1,24 @@
 module Faker
-  class Address
+  class Address < Base
     def self.zip_code
       Faker.numerify(["#####", "#####-####"].sample(Faker.rng))
     end
 
+    uniquify_builder(zip_code)
+
     {% for data_type in %w(state state_abbr city_suffix city_prefix country street_suffix country_code) %}
     def self.{{data_type.id}}
       Faker.fetch(Data["address"]["{{data_type.id}}"])
     end
+    uniquify_builder({{data_type.id}})
     {% end %}
 
     def self.city
       Faker.fetch(Data["address"]["city"])
     end
 
+    uniquify_builder(city)
+
     def self.street_name
       [
         ->{ [Name.last_name, street_suffix].join(" ") },
@@ -21,6 +26,8 @@ module Faker
       ].sample(Faker.rng).call
     end
 
+    uniquify_builder(street_name)
+
     def self.street_address
       Faker.numerify([
         ->{ "##### %s" % street_name },
@@ -32,14 +39,20 @@ module Faker
       ].sample(Faker.rng).call)
     end
 
+    uniquify_builder(street_address)
+
     def self.secondary_address
       Faker.numerify(Faker.fetch(Data["address"]["secondary_address"]))
     end
 
+    uniquify_builder(street_address)
+
     def self.building_number
       Faker.bothify(Faker.fetch(Data["address"]["building_number"]))
     end
 
+    uniquify_builder(building_number)
+
     def self.postcode
       Faker.bothify([
         ->{ "??# #??" },
@@ -47,16 +60,24 @@ module Faker
       ].sample(Faker.rng).call)
     end
 
+    uniquify_builder(postcode)
+
     def self.latitude
       ((Faker.rng.rand * 180) - 90).to_s
     end
 
+    uniquify_builder(latitude)
+
     def self.longitude
       ((Faker.rng.rand * 360) - 180).to_s
     end
 
+    uniquify_builder(longitude)
+
     def self.time_zone
       Faker.fetch(Data["address"]["time_zone"])
     end
+
+    uniquify_builder(time_zone)
   end
 end
diff --git a/src/faker/avatar.cr b/src/faker/avatar.cr
index 13d63e5..280d55c 100644
--- a/src/faker/avatar.cr
+++ b/src/faker/avatar.cr
@@ -1,8 +1,10 @@
 module Faker
-  class Avatar
+  class Avatar < Base
     def self.image(slug = nil)
       slug ||= Faker::Lorem.word
       "http://robohash.org/#{slug}"
     end
+
+    uniquify_builder(image, slug = nil)
   end
 end
diff --git a/src/faker/base.cr b/src/faker/base.cr
new file mode 100644
index 0000000..5b4fe3a
--- /dev/null
+++ b/src/faker/base.cr
@@ -0,0 +1,25 @@
+module Faker
+  class NonUniqueValue < Exception
+  end
+
+  class Base
+    alias Any = String | Int32 | Float64 | Time
+
+    macro uniquify_builder(attribute_name, *modified_method_attributes)
+      @@__unique_vals_for_{{attribute_name}} = Array(Any).new
+
+      def self.unique_{{attribute_name}}({% if !modified_method_attributes.empty? %}{{*modified_method_attributes}},{% end %} max_retries = 10_0000)
+        max_retries.times do |t|
+          val = self.{{attribute_name}}({{*modified_method_attributes}})
+
+          if !@@__unique_vals_for_{{attribute_name}}.includes?(val)
+            @@__unique_vals_for_{{attribute_name}} << val
+            return val
+          end
+        end
+
+        raise NonUniqueValue.new("Unable to generate unique value for {{attribute_name}}")
+      end
+    end
+  end
+end
diff --git a/src/faker/business.cr b/src/faker/business.cr
index 01179aa..f62cde3 100644
--- a/src/faker/business.cr
+++ b/src/faker/business.cr
@@ -1,16 +1,22 @@
 module Faker
-  class Business
+  class Business < Base
     def self.credit_card_number
       Faker.fetch(Data["business"]["credit_card_numbers"])
     end
 
+    uniquify_builder(credit_card_number)
+
     def self.credit_card_expiry_date
       credit_card_expiry_date = Faker.fetch(Data["business"]["credit_card_expiry_dates"]).as String
       Time.parse_local(credit_card_expiry_date, "%Y-%m-%d")
     end
 
+    uniquify_builder(credit_card_expiry_date)
+
     def self.credit_card_type
       Faker.fetch(Data["business"]["credit_card_types"])
     end
+
+    uniquify_builder(credit_card_type)
   end
 end
diff --git a/src/faker/commerce.cr b/src/faker/commerce.cr
index 92426a3..4e42e36 100644
--- a/src/faker/commerce.cr
+++ b/src/faker/commerce.cr
@@ -1,9 +1,11 @@
 module Faker
-  class Commerce
+  class Commerce < Base
     def self.color
       Faker.fetch(Data["color"]["name"])
     end
 
+    uniquify_builder(color)
+
     def self.department(max = 3, fixed_amount = false)
       num = max if fixed_amount
       num ||= 1 + Faker.rng.rand(max)
@@ -17,20 +19,28 @@ module Faker
       end
     end
 
+    uniquify_builder(department, max = 3, fixed_amount = false)
+
     def self.material
       product_name = Data["commerce"]["product_name"].as Hash
       Faker.fetch(product_name["material"])
     end
 
+    uniquify_builder(material)
+
     def self.product_name
       product_name = Data["commerce"]["product_name"].as Hash
       Faker.fetch(product_name["adjective"]) + " " + Faker.fetch(product_name["material"]) + " " + Faker.fetch(product_name["product"])
     end
 
+    uniquify_builder(product_name)
+
     def self.price(range = 0.0..100.0)
       (Faker.rng.rand(range) * 100).floor/100.0
     end
 
+    uniquify_builder(price, range = 0.0..100.0)
+
     private def self.categories(num)
       categories = [] of String
       while categories.size < num
diff --git a/src/faker/company.cr b/src/faker/company.cr
index 22e4874..d5d581e 100644
--- a/src/faker/company.cr
+++ b/src/faker/company.cr
@@ -1,26 +1,36 @@
 module Faker
-  class Company
+  class Company < Base
     def self.name
       Faker.fetch(Data["company"]["name"])
     end
 
+    uniquify_builder(name)
+
     def self.suffix
       Faker.fetch(Data["company"]["suffix"])
     end
 
+    uniquify_builder(suffix)
+
     def self.catch_phrase
       data = Data["company"]["buzzwords"].as Array(Array(String))
       Faker.fetch(data.flatten)
     end
 
+    uniquify_builder(catch_phrase)
+
     def self.bs
       data = Data["company"]["bs"].as Array(Array(String))
       Faker.fetch(data.flatten)
     end
 
+    uniquify_builder(bs)
+
     def self.logo
       rand_num = Faker.rng.rand(13) + 1
       "https://pigment.github.io/fake-logos/logos/medium/color/#{rand_num}.png"
     end
+
+    uniquify_builder(logo)
   end
 end
diff --git a/src/faker/finance.cr b/src/faker/finance.cr
index 2b78951..6063167 100644
--- a/src/faker/finance.cr
+++ b/src/faker/finance.cr
@@ -1,5 +1,5 @@
 module Faker
-  class Finance
+  class Finance < Base
     CREDIT_CARD_TYPES = (Data["credit_card"].as(Hash)).keys
 
     def self.credit_card(types : Array = [] of Array(String))
@@ -21,5 +21,6 @@ module Faker
       template = template.gsub "L", luhn_digit.to_s
       template
     end
+    # TODO: uniquify_builder(credit_card, types : Array = [] of Array(String))
   end
 end
diff --git a/src/faker/hacker.cr b/src/faker/hacker.cr
index 7f6cfb9..c5ddec1 100644
--- a/src/faker/hacker.cr
+++ b/src/faker/hacker.cr
@@ -1,14 +1,17 @@
 # Port of http://shinytoylabs.com/jargon/
 module Faker
-  class Hacker
+  class Hacker < Base
     def self.say_something_smart
       phrases.sample(Faker.rng)
     end
 
+    uniquify_builder(say_something_smart)
+
     {% for data_type in %w(abbreviation adjective noun verb ingverb) %}
       def self.{{data_type.id}}
         Faker.fetch(Data["hacker"]["{{data_type.id}}"])
       end
+      uniquify_builder({{data_type.id}})
     {% end %}
 
     def self.phrases
diff --git a/src/faker/internet.cr b/src/faker/internet.cr
index a4f21d3..10ee564 100644
--- a/src/faker/internet.cr
+++ b/src/faker/internet.cr
@@ -1,17 +1,23 @@
 module Faker
-  class Internet
+  class Internet < Base
     def self.email(name = nil)
       [user_name(name), domain_name].join("@")
     end
 
+    uniquify_builder(email, name = nil)
+
     def self.free_email(name = nil)
       [user_name(name), Faker.fetch(Data["internet"]["free_email"])].join("@")
     end
 
+    uniquify_builder(free_email, name = nil)
+
     def self.safe_email(name = nil)
       [user_name(name), "example." + %w(org com net).shuffle(Faker.rng).first].join("@")
     end
 
+    uniquify_builder(safe_email, name = nil)
+
     def self.user_name(specifier = nil, separators = %w(. _))
       if specifier.is_a? String
         return specifier.scan(/\w+/).map { |s| s[0] }.shuffle(Faker.rng).join(separators.sample(Faker.rng)).downcase
@@ -51,18 +57,26 @@ module Faker
       ].sample(Faker.rng).call
     end
 
+    uniquify_builder(user_name, specifier = nil, separators = %w(. _))
+
     def self.domain_name
       [domain_word, domain_suffix].join(".")
     end
 
+    uniquify_builder(domain_name)
+
     def self.domain_word
       Company.name.split(" ").first.gsub(/\W/, "").downcase
     end
 
+    uniquify_builder(domain_word)
+
     def self.domain_suffix
       Faker.fetch(Data["internet"]["domain_suffix"])
     end
 
+    uniquify_builder(domain_suffix)
+
     def self.ip_v4_address
       [
         (2..254).to_a.sample(Faker.rng),
@@ -72,27 +86,37 @@ module Faker
       ].join('.')
     end
 
+    uniquify_builder(ip_v4_address)
+
     def self.ip_v6_address
       ip_v6_space = (0..65535).to_a
       container = (1..8).map { |_| ip_v6_space.sample(Faker.rng) }
       container.map { |n| n.to_s(16) }.join(':')
     end
 
+    uniquify_builder(ip_v6_address)
+
     def self.mac_address(prefix = "")
       prefix_digits = prefix.split(":").map { |d| d.to_i?(16) ? d.to_i?(16) : 0 }
       address_digits = (1..(6 - prefix_digits.size)).map { Faker.rng.rand(256) }
       (prefix_digits + address_digits).map { |d| "%02x" % d }.join(":")
     end
 
+    uniquify_builder(mac_address, prefix = "")
+
     def self.url(host = domain_name, path = "/#{user_name}")
       "http://#{host}#{path}"
     end
 
+    uniquify_builder(url, host = domain_name, path = "/#{user_name}")
+
     def self.slug(words = nil, glue = nil)
       glue ||= %w(- _ .).sample(Faker.rng)
       (words || Lorem.words(2).join(' ')).gsub(' ', glue).downcase
     end
 
+    uniquify_builder(slug, words = nil, glue = nil)
+
     def self.password(min_length = 8, max_length = 16, mix_case = true, special_chars = false)
       temp = Lorem.characters(min_length)
       diff_length = max_length - min_length
@@ -115,5 +139,7 @@ module Faker
 
       return temp
     end
+
+    uniquify_builder(password, min_length = 8, max_length = 16, mix_case = true, special_chars = false)
   end
 end
diff --git a/src/faker/lorem.cr b/src/faker/lorem.cr
index f69711f..6ed5bf5 100644
--- a/src/faker/lorem.cr
+++ b/src/faker/lorem.cr
@@ -1,20 +1,26 @@
 module Faker
   # Based on Perl"s Text::Lorem
-  class Lorem
+  class Lorem < Base
     def self.character
       characters(1)
     end
 
+    uniquify_builder(character)
+
     def self.characters(char_count = 255)
       chars = ("a".."z").to_a + (0..9).to_a
       Array(String).new(char_count < 0 ? 0 : char_count, "").map { chars.sample(Faker.rng) }.join("")
     end
 
+    uniquify_builder(characters)
+
     def self.word
       words = Data["lorem"]["words"].as Array
       Faker.fetch(words)
     end
 
+    uniquify_builder(word)
+
     def self.words(num = 3, supplemental = false)
       words = Data["lorem"]["words"].as Array(String)
       words += (Data["lorem"]["supplemental"].as Array(String)) if supplemental
@@ -22,10 +28,14 @@ module Faker
       words.shuffle(Faker.rng)[0, num]
     end
 
+    uniquify_builder(words)
+
     def self.sentence(word_count = 4, supplemental = false, random_words_to_add = 6)
       words(word_count + Faker.rng.rand(random_words_to_add.to_i).to_i, supplemental).join(" ").capitalize + "."
     end
 
+    uniquify_builder(sentence)
+
     def self.sentences(sentence_count = 3, supplemental = false)
       ([] of String).tap do |sentences|
         1.upto(sentence_count) do
@@ -34,10 +44,14 @@ module Faker
       end
     end
 
+    uniquify_builder(sentences)
+
     def self.paragraph(sentence_count = 3, supplemental = false, random_sentences_to_add = 3)
       sentences(sentence_count + Faker.rng.rand(random_sentences_to_add.to_i).to_i, supplemental).join(" ")
     end
 
+    uniquify_builder(paragraph)
+
     def self.paragraphs(paragraph_count = 3, supplemental = false)
       ([] of String).tap do |paragraphs|
         1.upto(paragraph_count) do
@@ -45,5 +59,7 @@ module Faker
         end
       end
     end
+
+    uniquify_builder(paragraphs)
   end
 end
diff --git a/src/faker/name.cr b/src/faker/name.cr
index 007fec0..69ddce5 100644
--- a/src/faker/name.cr
+++ b/src/faker/name.cr
@@ -1,14 +1,17 @@
 module Faker
-  class Name
+  class Name < Base
     {% for data_type in %w(first_name last_name name prefix suffix) %}
       def self.{{data_type.id}}
         Faker.fetch(Data["name"]["{{data_type.id}}"])
       end
+      uniquify_builder({{data_type.id}})
     {% end %}
 
     def self.title
       title = Data["name"]["title"].as Hash
       Faker.fetch(title["descriptor"]) + " " + Faker.fetch(title["level"]) + " " + Faker.fetch(title["job"])
     end
+
+    uniquify_builder(title)
   end
 end
diff --git a/src/faker/number.cr b/src/faker/number.cr
index 1f68446..20c05d8 100644
--- a/src/faker/number.cr
+++ b/src/faker/number.cr
@@ -1,39 +1,53 @@
 module Faker
-  class Number
+  class Number < Base
     def self.number(digits)
       (1..digits).map { digit }.join ""
     end
 
+    uniquify_builder(number, digits)
+
     def self.digit
       Faker.rng.rand(10).to_s
     end
 
+    uniquify_builder(digit)
+
     def self.decimal(l_digits, r_digits = 2)
       l_d = number(l_digits)
       r_d = number(r_digits)
       "#{l_d}.#{r_d}"
     end
 
+    uniquify_builder(decimal, l_digits, r_digits = 2)
+
     def self.between(from = 1.00, to = 5000.00)
       Faker.rand_in_range(from, to)
     end
 
+    uniquify_builder(between)
+
     def self.positive(from = 1.00, to = 5000.00)
       random_number = between(from, to)
       greater_than_zero(random_number)
     end
 
+    uniquify_builder(positive)
+
     def self.negative(from = -5000.00, to = -1.00)
       random_number = between(from, to)
       less_than_zero(random_number)
     end
 
+    uniquify_builder(negative)
+
     def self.hexadecimal(digits)
       hex = ""
       digits.times { hex += Faker.rng.rand(15).to_s(16) }
       hex
     end
 
+    uniquify_builder(hexadecimal)
+
     private def self.greater_than_zero(number)
       if number > 0
         number
diff --git a/src/faker/phone_number.cr b/src/faker/phone_number.cr
index 699b0d6..7f9ddb9 100644
--- a/src/faker/phone_number.cr
+++ b/src/faker/phone_number.cr
@@ -1,7 +1,9 @@
 module Faker
-  class PhoneNumber
+  class PhoneNumber < Base
     def self.phone_number
       Faker.numerify(Faker.fetch(Data["phone_number"]["formats"]))
     end
+
+    uniquify_builder(phone_number)
   end
 end
diff --git a/src/faker/team.cr b/src/faker/team.cr
index fb4779f..453785e 100644
--- a/src/faker/team.cr
+++ b/src/faker/team.cr
@@ -1,15 +1,21 @@
 module Faker
-  class Team
+  class Team < Base
     def self.name
       Faker.fetch(Data["team"]["name"])
     end
 
+    uniquify_builder(name)
+
     def self.creature
       Faker.fetch(Data["team"]["creature"])
     end
 
+    uniquify_builder(creature)
+
     def self.state
       Faker.fetch(Data["address"]["state"])
     end
+
+    uniquify_builder(state)
   end
 end