diff --git a/lib/ansible/playbook/conditional.py b/lib/ansible/playbook/conditional.py
index e0c426df3be..1a1cc4f9762 100644
--- a/lib/ansible/playbook/conditional.py
+++ b/lib/ansible/playbook/conditional.py
@@ -19,6 +19,8 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
+import re
+
 from jinja2.exceptions import UndefinedError
 
 from ansible.compat.six import text_type
@@ -27,6 +29,8 @@ from ansible.playbook.attribute import FieldAttribute
 from ansible.template import Templar
 from ansible.module_utils._text import to_native
 
+DEFINED_REGEX = re.compile(r'(hostvars\[.+\]|[\w_]+)\s+(not\s+is|is|is\s+not)\s+(defined|undefined)')
+
 class Conditional:
 
     '''
@@ -62,6 +66,18 @@ class Conditional:
             when = self._get_parent_attribute('when', extend=True, prepend=True)
         return when
 
+    def extract_defined_undefined(self, conditional):
+        results = []
+
+        cond = conditional
+        m = DEFINED_REGEX.search(cond)
+        while m:
+            results.append(m.groups())
+            cond = cond[m.end():]
+            m = DEFINED_REGEX.search(cond)
+
+        return results
+
     def evaluate_conditional(self, templar, all_vars):
         '''
         Loops through the conditionals set on this object, returning
@@ -121,14 +137,31 @@ class Conditional:
             else:
                 raise AnsibleError("unable to evaluate conditional: %s" % original)
         except (AnsibleUndefinedVariable, UndefinedError) as e:
-            # the templating failed, meaning most likely a
-            # variable was undefined. If we happened to be
-            # looking for an undefined variable, return True,
-            # otherwise fail
-            if "is undefined" in original or "is not defined" in original or "not is defined" in original:
-                return True
-            elif "is defined" in original or "is not undefined" in original or "not is undefined" in original:
-                return False
-            else:
+            # the templating failed, meaning most likely a variable was undefined. If we happened to be
+            # looking for an undefined variable, return True, otherwise fail
+            try:
+                # first we extract the variable name from the error message
+                var_name = re.compile(r"'(hostvars\[.+\]|[\w_]+)' is undefined").search(str(e)).groups()[0]
+                # next we extract all defined/undefined tests from the conditional string
+                def_undef = self.extract_defined_undefined(conditional)
+                # then we loop through these, comparing the error variable name against
+                # each def/undef test we found above. If there is a match, we determine
+                # whether the logic/state mean the variable should exist or not and return
+                # the corresponding True/False
+                for (du_var, logic, state) in def_undef:
+                    # when we compare the var names, normalize quotes because something
+                    # like hostvars['foo'] may be tested against hostvars["foo"]
+                    if var_name.replace("'", '"') == du_var.replace("'", '"'):
+                        # the should exist is a xor test between a negation in the logic portion
+                        # against the state (defined or undefined)
+                        should_exist = ('not' in logic) != (state == 'defined')
+                        if should_exist:
+                            return False
+                        else:
+                            return True
+                # as nothing above matched the failed var name, re-raise here to
+                # trigger the AnsibleUndefinedVariable exception again below
+                raise
+            except Exception as new_e:
                 raise AnsibleUndefinedVariable("error while evaluating conditional (%s): %s" % (original, e))
 
diff --git a/lib/ansible/vars/hostvars.py b/lib/ansible/vars/hostvars.py
index 74262b2ed46..3922b827a7b 100644
--- a/lib/ansible/vars/hostvars.py
+++ b/lib/ansible/vars/hostvars.py
@@ -73,7 +73,7 @@ class HostVars(collections.Mapping):
         '''
         host = self._find_host(host_name)
         if host is None:
-            raise UndefinedError("%s not found in hostvars" % host_name)
+            raise UndefinedError("'hostvars[\"%s\"]' is undefined" % host_name)
 
         return self._variable_manager.get_vars(loader=self._loader, host=host, include_hostvars=False)