diff --git a/lib/puppet/parser/functions/bool2str.rb b/lib/puppet/parser/functions/bool2str.rb
index a97d356ab..fcd379178 100644
--- a/lib/puppet/parser/functions/bool2str.rb
+++ b/lib/puppet/parser/functions/bool2str.rb
@@ -5,7 +5,7 @@
 module Puppet::Parser::Functions
   newfunction(:bool2str, :type => :rvalue, :doc => <<-EOS
     Converts a boolean to a string.
-    Requires a single boolean or string as an input.
+    Requires a single boolean as an input.
     EOS
   ) do |arguments|
 
@@ -15,15 +15,12 @@ module Puppet::Parser::Functions
     value = arguments[0]
     klass = value.class
 
-    # We can have either true or false, or string which resembles boolean ...
-    unless [FalseClass, TrueClass, String].include?(klass)
-      raise(Puppet::ParseError, 'bool2str(): Requires either ' +
-        'boolean or string to work with')
+    # We can have either true or false, and nothing else
+    unless [FalseClass, TrueClass].include?(klass)
+      raise(Puppet::ParseError, 'bool2str(): Requires a boolean to work with')
     end
 
-    result = value.is_a?(String) ? value : value.to_s
-
-    return result
+    return value.to_s
   end
 end
 
diff --git a/spec/unit/puppet/parser/functions/bool2str_spec.rb b/spec/unit/puppet/parser/functions/bool2str_spec.rb
index c73f7df11..bed7e68a0 100755
--- a/spec/unit/puppet/parser/functions/bool2str_spec.rb
+++ b/spec/unit/puppet/parser/functions/bool2str_spec.rb
@@ -31,4 +31,16 @@
     result = scope.function_bool2str([false])
     result.class.should(eq(String))
   end
+
+  it "should not accept a string" do
+    lambda { scope.function_bool2str(["false"]) }.should( raise_error(Puppet::ParseError))
+  end
+
+  it "should not accept a nil value" do
+    lambda { scope.function_bool2str([nil]) }.should( raise_error(Puppet::ParseError))
+  end
+
+  it "should not accept an undef" do
+    lambda { scope.function_bool2str([:undef]) }.should( raise_error(Puppet::ParseError))
+  end
 end