diff --git a/lib/puppet/parser/functions/bool2num.rb b/lib/puppet/parser/functions/bool2num.rb
index 9a07a8a11..b32a4e87d 100644
--- a/lib/puppet/parser/functions/bool2num.rb
+++ b/lib/puppet/parser/functions/bool2num.rb
@@ -15,10 +15,9 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
     # We can have either true or false, or string which resembles boolean ...
-    unless [FalseClass, TrueClass, String].include?(klass)
+    unless value.is_a?(String) || value.is_a?(FalseClass) || value.is_a?(TrueClass)
       raise(Puppet::ParseError, 'bool2num(): Requires either ' +
         'boolean or string to work with')
     end
diff --git a/lib/puppet/parser/functions/capitalize.rb b/lib/puppet/parser/functions/capitalize.rb
index 640d00b82..98b2d16c9 100644
--- a/lib/puppet/parser/functions/capitalize.rb
+++ b/lib/puppet/parser/functions/capitalize.rb
@@ -13,9 +13,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'capitalize(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/chomp.rb b/lib/puppet/parser/functions/chomp.rb
index 4564a000a..c55841e3c 100644
--- a/lib/puppet/parser/functions/chomp.rb
+++ b/lib/puppet/parser/functions/chomp.rb
@@ -14,9 +14,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'chomp(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/chop.rb b/lib/puppet/parser/functions/chop.rb
index f242af39c..b24ab7856 100644
--- a/lib/puppet/parser/functions/chop.rb
+++ b/lib/puppet/parser/functions/chop.rb
@@ -16,9 +16,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'chop(): Requires either an ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/downcase.rb b/lib/puppet/parser/functions/downcase.rb
index 4066d210f..040b84f56 100644
--- a/lib/puppet/parser/functions/downcase.rb
+++ b/lib/puppet/parser/functions/downcase.rb
@@ -12,9 +12,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'downcase(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/empty.rb b/lib/puppet/parser/functions/empty.rb
index 80ebb86b8..cca620fae 100644
--- a/lib/puppet/parser/functions/empty.rb
+++ b/lib/puppet/parser/functions/empty.rb
@@ -12,9 +12,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, Hash, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(Hash) || value.is_a?(String)
       raise(Puppet::ParseError, 'empty(): Requires either ' +
         'array, hash or string to work with')
     end
diff --git a/lib/puppet/parser/functions/fqdn_rotate.rb b/lib/puppet/parser/functions/fqdn_rotate.rb
index 655820605..7f4d37d01 100644
--- a/lib/puppet/parser/functions/fqdn_rotate.rb
+++ b/lib/puppet/parser/functions/fqdn_rotate.rb
@@ -12,10 +12,9 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
     require 'digest/md5'
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'fqdn_rotate(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/lstrip.rb b/lib/puppet/parser/functions/lstrip.rb
index 3a64de337..624e4c846 100644
--- a/lib/puppet/parser/functions/lstrip.rb
+++ b/lib/puppet/parser/functions/lstrip.rb
@@ -12,9 +12,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'lstrip(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/reverse.rb b/lib/puppet/parser/functions/reverse.rb
index fe048690c..7f1018f67 100644
--- a/lib/puppet/parser/functions/reverse.rb
+++ b/lib/puppet/parser/functions/reverse.rb
@@ -12,9 +12,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'reverse(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/rstrip.rb b/lib/puppet/parser/functions/rstrip.rb
index 29b099820..0cf8d222c 100644
--- a/lib/puppet/parser/functions/rstrip.rb
+++ b/lib/puppet/parser/functions/rstrip.rb
@@ -12,9 +12,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'rstrip(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/shuffle.rb b/lib/puppet/parser/functions/shuffle.rb
index 18134ab63..30c663dbe 100644
--- a/lib/puppet/parser/functions/shuffle.rb
+++ b/lib/puppet/parser/functions/shuffle.rb
@@ -12,9 +12,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'shuffle(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/strip.rb b/lib/puppet/parser/functions/strip.rb
index 5f4630d7d..3fac47d53 100644
--- a/lib/puppet/parser/functions/strip.rb
+++ b/lib/puppet/parser/functions/strip.rb
@@ -19,9 +19,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'strip(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/swapcase.rb b/lib/puppet/parser/functions/swapcase.rb
index b9e663253..eb7fe137d 100644
--- a/lib/puppet/parser/functions/swapcase.rb
+++ b/lib/puppet/parser/functions/swapcase.rb
@@ -18,9 +18,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'swapcase(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/unique.rb b/lib/puppet/parser/functions/unique.rb
index 8844a7418..cf770f3b4 100644
--- a/lib/puppet/parser/functions/unique.rb
+++ b/lib/puppet/parser/functions/unique.rb
@@ -28,9 +28,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'unique(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/upcase.rb b/lib/puppet/parser/functions/upcase.rb
index fe6cadc3c..4302b29e7 100644
--- a/lib/puppet/parser/functions/upcase.rb
+++ b/lib/puppet/parser/functions/upcase.rb
@@ -20,9 +20,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'upcase(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/uriescape.rb b/lib/puppet/parser/functions/uriescape.rb
index 0d81de5d1..a486eee50 100644
--- a/lib/puppet/parser/functions/uriescape.rb
+++ b/lib/puppet/parser/functions/uriescape.rb
@@ -14,9 +14,8 @@ module Puppet::Parser::Functions
       "given (#{arguments.size} for 1)") if arguments.size < 1
 
     value = arguments[0]
-    klass = value.class
 
-    unless [Array, String].include?(klass)
+    unless value.is_a?(Array) || value.is_a?(String)
       raise(Puppet::ParseError, 'uriescape(): Requires either ' +
         'array or string to work with')
     end
diff --git a/lib/puppet/parser/functions/zip.rb b/lib/puppet/parser/functions/zip.rb
index 2b56e9ca0..00266a4c5 100644
--- a/lib/puppet/parser/functions/zip.rb
+++ b/lib/puppet/parser/functions/zip.rb
@@ -30,10 +30,8 @@ module Puppet::Parser::Functions
     flatten = arguments[2] if arguments[2]
 
     if flatten
-      klass = flatten.class
-
       # We can have either true or false, or string which resembles boolean ...
-      unless [FalseClass, TrueClass, String].include?(klass)
+      unless flatten.is_a?(String) || flatten.is_a?(FalseClass) || flatten.is_a?(TrueClass)
         raise(Puppet::ParseError, 'zip(): Requires either ' +
           'boolean or string to work with')
       end
diff --git a/spec/functions/bool2num_spec.rb b/spec/functions/bool2num_spec.rb
index fbf461b14..3904d7e40 100755
--- a/spec/functions/bool2num_spec.rb
+++ b/spec/functions/bool2num_spec.rb
@@ -17,8 +17,22 @@
     expect(result).to(eq(1))
   end
 
-  it "should convert false to 0" do
-    result = scope.function_bool2num([false])
+  it "should convert 'true' to 1" do
+    result = scope.function_bool2num(['true'])
+    result.should(eq(1))
+  end
+
+  it "should convert 'false' to 0" do
+    result = scope.function_bool2num(['false'])
     expect(result).to(eq(0))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('true')
+    result = scope.function_bool2num([value])
+    result.should(eq(1))
+  end
 end
diff --git a/spec/functions/capitalize_spec.rb b/spec/functions/capitalize_spec.rb
index 0cc2d760b..fd0e92ba2 100755
--- a/spec/functions/capitalize_spec.rb
+++ b/spec/functions/capitalize_spec.rb
@@ -16,4 +16,13 @@
     result = scope.function_capitalize(["abc"])
     expect(result).to(eq("Abc"))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('abc')
+    result = scope.function_capitalize([value])
+    result.should(eq('Abc'))
+  end
 end
diff --git a/spec/functions/chomp_spec.rb b/spec/functions/chomp_spec.rb
index d2ae28749..b1e1e60f3 100755
--- a/spec/functions/chomp_spec.rb
+++ b/spec/functions/chomp_spec.rb
@@ -16,4 +16,13 @@
     result = scope.function_chomp(["abc\n"])
     expect(result).to(eq("abc"))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new("abc\n")
+    result = scope.function_chomp([value])
+    result.should(eq("abc"))
+  end
 end
diff --git a/spec/functions/chop_spec.rb b/spec/functions/chop_spec.rb
index d9dbb88a5..c8a19519a 100755
--- a/spec/functions/chop_spec.rb
+++ b/spec/functions/chop_spec.rb
@@ -16,4 +16,13 @@
     result = scope.function_chop(["asdf\n"])
     expect(result).to(eq("asdf"))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new("abc\n")
+    result = scope.function_chop([value])
+    result.should(eq('abc'))
+  end
 end
diff --git a/spec/functions/downcase_spec.rb b/spec/functions/downcase_spec.rb
index a844780b1..edebc44f1 100755
--- a/spec/functions/downcase_spec.rb
+++ b/spec/functions/downcase_spec.rb
@@ -21,4 +21,13 @@
     result = scope.function_downcase(["asdf asdf"])
     expect(result).to(eq("asdf asdf"))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new("ASFD")
+    result = scope.function_downcase([value])
+    result.should(eq('asfd'))
+  end
 end
diff --git a/spec/functions/empty_spec.rb b/spec/functions/empty_spec.rb
index 1f2ace4ca..6a97c4cd3 100755
--- a/spec/functions/empty_spec.rb
+++ b/spec/functions/empty_spec.rb
@@ -20,4 +20,13 @@
     result = scope.function_empty(['asdf'])
     expect(result).to(eq(false))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new()
+    result = scope.function_empty([value])
+    result.should(eq(true))
+  end
 end
diff --git a/spec/functions/fqdn_rotate_spec.rb b/spec/functions/fqdn_rotate_spec.rb
index b2dc1f5a3..40057d4f7 100755
--- a/spec/functions/fqdn_rotate_spec.rb
+++ b/spec/functions/fqdn_rotate_spec.rb
@@ -30,4 +30,14 @@
      val2 = scope.function_fqdn_rotate(["abcdefghijklmnopqrstuvwxyz01234567890987654321"])
      expect(val1).not_to eql(val2)
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    scope.expects(:lookupvar).with("::fqdn").returns("127.0.0.1")
+    value = AlsoString.new("asdf")
+    result = scope.function_fqdn_rotate([value])
+    result.size.should(eq(4))
+  end
 end
diff --git a/spec/functions/lstrip_spec.rb b/spec/functions/lstrip_spec.rb
index 7025f97b8..68cca1c5d 100755
--- a/spec/functions/lstrip_spec.rb
+++ b/spec/functions/lstrip_spec.rb
@@ -16,4 +16,13 @@
     result = scope.function_lstrip(["  asdf"])
     expect(result).to(eq('asdf'))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new("  asdf")
+    result = scope.function_lstrip([value])
+    result.should(eq("asdf"))
+  end
 end
diff --git a/spec/functions/reverse_spec.rb b/spec/functions/reverse_spec.rb
index bfeabfb84..1f047943f 100755
--- a/spec/functions/reverse_spec.rb
+++ b/spec/functions/reverse_spec.rb
@@ -16,4 +16,13 @@
     result = scope.function_reverse(["asdfghijkl"])
     expect(result).to(eq('lkjihgfdsa'))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('asdfghjkl')
+    result = scope.function_reverse([value])
+    result.should(eq('lkjhgfdsa'))
+  end
 end
diff --git a/spec/functions/rstrip_spec.rb b/spec/functions/rstrip_spec.rb
index 81321d766..f6b483896 100755
--- a/spec/functions/rstrip_spec.rb
+++ b/spec/functions/rstrip_spec.rb
@@ -21,4 +21,13 @@
     result = scope.function_rstrip([["a ","b ", "c "]])
     expect(result).to(eq(['a','b','c']))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('asdf ')
+    result = scope.function_rstrip([value])
+    result.should(eq('asdf'))
+  end
 end
diff --git a/spec/functions/shuffle_spec.rb b/spec/functions/shuffle_spec.rb
index ee0e2ffb2..a62c1fb5e 100755
--- a/spec/functions/shuffle_spec.rb
+++ b/spec/functions/shuffle_spec.rb
@@ -21,4 +21,13 @@
     result = scope.function_shuffle(["adfs"])
     expect(result.split("").sort.join("")).to(eq("adfs"))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('asdf')
+    result = scope.function_shuffle([value])
+    result.size.should(eq(4))
+  end
 end
diff --git a/spec/functions/strip_spec.rb b/spec/functions/strip_spec.rb
index e228761d0..4ac8daf86 100755
--- a/spec/functions/strip_spec.rb
+++ b/spec/functions/strip_spec.rb
@@ -15,4 +15,13 @@
     result = scope.function_strip([" ab cd "])
     expect(result).to(eq('ab cd'))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new(' as df ')
+    result = scope.function_strip([value])
+    result.should(eq('as df'))
+  end
 end
diff --git a/spec/functions/swapcase_spec.rb b/spec/functions/swapcase_spec.rb
index c6838ab4e..791d1dfae 100755
--- a/spec/functions/swapcase_spec.rb
+++ b/spec/functions/swapcase_spec.rb
@@ -16,4 +16,13 @@
     result = scope.function_swapcase(["aaBBccDD"])
     expect(result).to(eq('AAbbCCdd'))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new("aaBBccDD")
+    result = scope.function_swapcase([value])
+    result.should(eq("AAbbCCdd"))
+  end
 end
diff --git a/spec/functions/unique_spec.rb b/spec/functions/unique_spec.rb
index 8ec1464eb..7cd3a566f 100755
--- a/spec/functions/unique_spec.rb
+++ b/spec/functions/unique_spec.rb
@@ -21,4 +21,13 @@
     result = scope.function_unique([["a","a","b","b","c"]])
     expect(result).to(eq(['a','b','c']))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('aabbc')
+    result = scope.function_unique([value])
+    result.should(eq('abc'))
+  end
 end
diff --git a/spec/functions/upcase_spec.rb b/spec/functions/upcase_spec.rb
index 78e55ddf1..3cf8b0552 100755
--- a/spec/functions/upcase_spec.rb
+++ b/spec/functions/upcase_spec.rb
@@ -21,4 +21,13 @@
     result = scope.function_upcase(["ABC"])
     expect(result).to(eq('ABC'))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('abc')
+    result = scope.function_upcase([value])
+    result.should(eq('ABC'))
+  end
 end
diff --git a/spec/functions/uriescape_spec.rb b/spec/functions/uriescape_spec.rb
index c44e9c19b..2321e5aba 100755
--- a/spec/functions/uriescape_spec.rb
+++ b/spec/functions/uriescape_spec.rb
@@ -21,4 +21,13 @@
     result = scope.function_uriescape(["ABCdef"])
     expect(result).to(eq('ABCdef'))
   end
+
+  it "should accept objects which extend String" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('abc')
+    result = scope.function_uriescape([value])
+    result.should(eq('abc'))
+  end
 end
diff --git a/spec/functions/zip_spec.rb b/spec/functions/zip_spec.rb
index 744bdd786..f265fcee4 100755
--- a/spec/functions/zip_spec.rb
+++ b/spec/functions/zip_spec.rb
@@ -11,5 +11,21 @@
   it "should be able to zip an array" do
     result = scope.function_zip([['1','2','3'],['4','5','6']])
     expect(result).to(eq([["1", "4"], ["2", "5"], ["3", "6"]]))
+    result = scope.function_zip([['1','2','3'],['4','5','6'], false])
+    result.should(eq([["1", "4"], ["2", "5"], ["3", "6"]]))
+  end
+
+  it "should be able to zip an array and flatten" do
+    result = scope.function_zip([['1','2','3'],['4','5','6'], true])
+    result.should(eq(["1", "4", "2", "5", "3", "6"]))
+  end
+
+  it "should accept objects which extend String for the second argument" do
+    class AlsoString < String
+    end
+
+    value = AlsoString.new('false')
+    result = scope.function_zip([['1','2','3'],['4','5','6'],value])
+    result.should(eq([["1", "4"], ["2", "5"], ["3", "6"]]))
   end
 end