diff --git a/lib/cask/dsl.rb b/lib/cask/dsl.rb
index 14d6d63b81..426413f188 100644
--- a/lib/cask/dsl.rb
+++ b/lib/cask/dsl.rb
@@ -22,16 +22,25 @@ module Cask::DSL
 
   module ClassMethods
     def homepage(homepage=nil)
+      if @homepage and !homepage.nil?
+        raise CaskInvalidError.new(self.title, "'homepage' stanza may only appear once")
+      end
       @homepage ||= homepage
     end
 
     def url(*args)
+      if @url and !args.empty?
+        raise CaskInvalidError.new(self.title, "'url' stanza may only appear once")
+      end
       @url ||= begin
         Cask::URL.new(*args) unless args.empty?
       end
     end
 
     def version(version=nil)
+      if @version and !version.nil?
+        raise CaskInvalidError.new(self.title, "'version' stanza may only appear once")
+      end
       @version ||= version
     end
 
@@ -100,22 +109,38 @@ module Cask::DSL
 
     attr_reader :sums
 
+    def hash_name(hash_type)
+      hash_type.to_s == 'sha2' ? 'sha256' : hash_type.to_s
+    end
+
     def md5(md5=nil)
+      if @sums == 0
+        raise CaskInvalidError.new(self.title, "'no_checksum' stanza conflicts with 'md5'")
+      end
       @sums ||= []
       @sums << Checksum.new(:md5, md5) unless md5.nil?
     end
 
     def sha1(sha1=nil)
+      if @sums == 0
+        raise CaskInvalidError.new(self.title, "'no_checksum' stanza conflicts with 'sha1'")
+      end
       @sums ||= []
       @sums << Checksum.new(:sha1, sha1) unless sha1.nil?
     end
 
     def sha256(sha2=nil)
+      if @sums == 0
+        raise CaskInvalidError.new(self.title, "'no_checksum' stanza conflicts with 'sha256'")
+      end
       @sums ||= []
       @sums << Checksum.new(:sha2, sha2) unless sha2.nil?
     end
 
     def no_checksum
+      unless @sums.nil? or @sums.empty?
+        raise CaskInvalidError.new(self.title, "'no_checksum' stanza conflicts with '#{hash_name(@sums.first.hash_type)}'")
+      end
       @sums = 0
     end
 
diff --git a/lib/cask/exceptions.rb b/lib/cask/exceptions.rb
index 12f4f028e3..ff19c265d1 100644
--- a/lib/cask/exceptions.rb
+++ b/lib/cask/exceptions.rb
@@ -68,3 +68,15 @@ class CaskUnspecifiedError < CaskError
     "This command requires a cask's name"
   end
 end
+
+class CaskInvalidError < CaskError
+  attr_reader :name, :submsg
+  def initialize(name, *submsg)
+    @name = name
+    @submsg = submsg.join(' ')
+  end
+
+  def to_s
+    "Cask '#{name}' definition is invalid" + (submsg.length > 0 ? ": #{submsg}" : '')
+  end
+end
diff --git a/test/cask/dsl_test.rb b/test/cask/dsl_test.rb
index 1883e01a5a..4be0adcd84 100644
--- a/test/cask/dsl_test.rb
+++ b/test/cask/dsl_test.rb
@@ -92,4 +92,39 @@ describe Cask::DSL do
     instance = CaskWithInstallables.new
     Array(instance.artifacts[:install]).sort.must_equal %w[Bar.pkg Foo.pkg]
   end
+
+  it "prevents defining multiple urls" do
+    err = lambda {
+      invalid_cask = Cask.load('invalid/invalid-two-url')
+    }.must_raise(CaskInvalidError)
+    err.message.must_include "'url' stanza may only appear once"
+  end
+
+  it "prevents defining multiple homepages" do
+    err = lambda {
+      invalid_cask = Cask.load('invalid/invalid-two-homepage')
+    }.must_raise(CaskInvalidError)
+    err.message.must_include "'homepage' stanza may only appear once"
+  end
+
+  it "prevents defining multiple versions" do
+    err = lambda {
+      invalid_cask = Cask.load('invalid/invalid-two-version')
+    }.must_raise(CaskInvalidError)
+    err.message.must_include "'version' stanza may only appear once"
+  end
+
+  it "prevents defining conflicting checksums (first order)" do
+    err = lambda {
+      invalid_cask = Cask.load('invalid/invalid-checksum-conflict1')
+    }.must_raise(CaskInvalidError)
+    err.message.must_include "'no_checksum' stanza conflicts with"
+  end
+
+  it "prevents defining conflicting checksums (second order)" do
+    err = lambda {
+      invalid_cask = Cask.load('invalid/invalid-checksum-conflict2')
+    }.must_raise(CaskInvalidError)
+    err.message.must_include "'no_checksum' stanza conflicts with"
+  end
 end
diff --git a/test/cask_test.rb b/test/cask_test.rb
index 35fc014038..1c8e192125 100644
--- a/test/cask_test.rb
+++ b/test/cask_test.rb
@@ -9,6 +9,9 @@ describe "Cask" do
     end
 
     it "returns an instance of the cask from a specific file location" do
+      if Object.constants.include?(:Dia)
+        Object.send(:remove_const, :Dia)
+      end
       location = File.expand_path('./Casks/dia.rb')
       c = Cask.load(location)
       c.must_be_kind_of(Cask)
@@ -16,6 +19,9 @@ describe "Cask" do
     end
 
     it "returns an instance of the cask from a url" do
+      if Object.constants.include?(:Dia)
+        Object.send(:remove_const, :Dia)
+      end
       url = "file://" + File.expand_path('./Casks/dia.rb')
       c = shutup do
         Cask.load(url)
@@ -34,9 +40,12 @@ describe "Cask" do
     end
 
     it "returns an instance of the cask from a relative file location" do
-      c = Cask.load("./Casks/dia.rb")
+      if Object.constants.include?(:Bbedit)
+        Object.send(:remove_const, :Bbedit)
+      end
+      c = Cask.load("./Casks/bbedit.rb")
       c.must_be_kind_of(Cask)
-      c.must_be_instance_of(Dia)
+      c.must_be_instance_of(Bbedit)
     end
 
     it "uses exact match when loading by name" do
diff --git a/test/support/Casks/invalid/invalid-checksum-conflict1.rb b/test/support/Casks/invalid/invalid-checksum-conflict1.rb
new file mode 100644
index 0000000000..541aacb7c5
--- /dev/null
+++ b/test/support/Casks/invalid/invalid-checksum-conflict1.rb
@@ -0,0 +1,8 @@
+class InvalidChecksumConflict1 < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/local-caffeine'
+  version '1.2.3'
+  sha1 'd2fbdad1619934313026fc831e6c6e3dd97ac030'
+  no_checksum
+  link 'Caffeine.app'
+end
diff --git a/test/support/Casks/invalid/invalid-checksum-conflict2.rb b/test/support/Casks/invalid/invalid-checksum-conflict2.rb
new file mode 100644
index 0000000000..bc4c8ff2de
--- /dev/null
+++ b/test/support/Casks/invalid/invalid-checksum-conflict2.rb
@@ -0,0 +1,8 @@
+class InvalidChecksumConflict2 < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/local-caffeine'
+  version '1.2.3'
+  no_checksum
+  sha1 'd2fbdad1619934313026fc831e6c6e3dd97ac030'
+  link 'Caffeine.app'
+end
diff --git a/test/support/Casks/invalid/invalid-two-homepage.rb b/test/support/Casks/invalid/invalid-two-homepage.rb
new file mode 100644
index 0000000000..cd43c1d8f0
--- /dev/null
+++ b/test/support/Casks/invalid/invalid-two-homepage.rb
@@ -0,0 +1,9 @@
+class InvalidTwoHomepage < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/local-caffeine'
+  homepage 'http://www.example.com/local-caffeine'
+  version '1.2.3'
+  sha1 'd2fbdad1619934313026fc831e6c6e3dd97ac030'
+
+  link 'Caffeine.app'
+end
diff --git a/test/support/Casks/invalid/invalid-two-url.rb b/test/support/Casks/invalid/invalid-two-url.rb
new file mode 100644
index 0000000000..e3e0db2e63
--- /dev/null
+++ b/test/support/Casks/invalid/invalid-two-url.rb
@@ -0,0 +1,9 @@
+class InvalidTwoUrl < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  url 'http://example.com/caffeine.zip'
+  homepage 'http://example.com/local-caffeine'
+  version '1.2.3'
+  sha1 'd2fbdad1619934313026fc831e6c6e3dd97ac030'
+
+  link 'Caffeine.app'
+end
diff --git a/test/support/Casks/invalid/invalid-two-version.rb b/test/support/Casks/invalid/invalid-two-version.rb
new file mode 100644
index 0000000000..00f1aa0d6b
--- /dev/null
+++ b/test/support/Casks/invalid/invalid-two-version.rb
@@ -0,0 +1,9 @@
+class InvalidTwoVersion < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/local-caffeine'
+  version '1.2.3'
+  version '2.0'
+  sha1 'd2fbdad1619934313026fc831e6c6e3dd97ac030'
+
+  link 'Caffeine.app'
+end