diff --git a/lib/ansible/playbook/base.py b/lib/ansible/playbook/base.py
index fe4c0fe9e74..6c952128a98 100644
--- a/lib/ansible/playbook/base.py
+++ b/lib/ansible/playbook/base.py
@@ -482,7 +482,7 @@ class Base(with_metaclass(BaseMeta, object)):
         except TypeError as e:
             raise AnsibleParserError("Invalid variable name in vars specified for %s: %s" % (self.__class__.__name__, e), obj=ds)
 
-    def _extend_value(self, value, new_value):
+    def _extend_value(self, value, new_value, prepend=False):
         '''
         Will extend the value given with new_value (and will turn both
         into lists if they are not so already). The values are run through
@@ -494,7 +494,12 @@ class Base(with_metaclass(BaseMeta, object)):
         if not isinstance(new_value, list):
             new_value = [ new_value ]
 
-        return [i for i,_ in itertools.groupby(value + new_value) if i is not None]
+        if prepend:
+            combined = new_value + value
+        else:
+            combined = value + new_value
+
+        return [i for i,_ in itertools.groupby(combined) if i is not None]
 
     def serialize(self):
         '''
diff --git a/lib/ansible/playbook/block.py b/lib/ansible/playbook/block.py
index 7d6dab32f64..be04963704c 100644
--- a/lib/ansible/playbook/block.py
+++ b/lib/ansible/playbook/block.py
@@ -273,7 +273,7 @@ class Block(Base, Become, Conditional, Taggable):
     def _get_attr_environment(self):
         return self._get_parent_attribute('environment', extend=True)
 
-    def _get_parent_attribute(self, attr, extend=False):
+    def _get_parent_attribute(self, attr, extend=False, prepend=False):
         '''
         Generic logic to get the attribute or parent attribute for a block value.
         '''
@@ -286,7 +286,7 @@ class Block(Base, Become, Conditional, Taggable):
                 try:
                     parent_value = getattr(self._parent, attr, None)
                     if extend:
-                        value = self._extend_value(value, parent_value)
+                        value = self._extend_value(value, parent_value, prepend)
                     else:
                         value = parent_value
                 except AttributeError:
@@ -295,7 +295,7 @@ class Block(Base, Become, Conditional, Taggable):
                 try:
                     parent_value = getattr(self._role, attr, None)
                     if extend:
-                        value = self._extend_value(value, parent_value)
+                        value = self._extend_value(value, parent_value, prepend)
                     else:
                         value = parent_value
 
@@ -305,7 +305,7 @@ class Block(Base, Become, Conditional, Taggable):
                         for dep in dep_chain:
                             dep_value = getattr(dep, attr, None)
                             if extend:
-                                value = self._extend_value(value, dep_value)
+                                value = self._extend_value(value, dep_value, prepend)
                             else:
                                 value = dep_value
 
@@ -317,7 +317,7 @@ class Block(Base, Become, Conditional, Taggable):
                 try:
                     parent_value = getattr(self._play, attr, None)
                     if extend:
-                        value = self._extend_value(value, parent_value)
+                        value = self._extend_value(value, parent_value, prepend)
                     else:
                         value = parent_value
                 except AttributeError:
diff --git a/lib/ansible/playbook/conditional.py b/lib/ansible/playbook/conditional.py
index 0fada8258c9..0efe9f4a76f 100644
--- a/lib/ansible/playbook/conditional.py
+++ b/lib/ansible/playbook/conditional.py
@@ -59,7 +59,7 @@ class Conditional:
         if when is None:
             when = []
         if hasattr(self, '_get_parent_attribute'):
-            when = self._get_parent_attribute('when', extend=True)
+            when = self._get_parent_attribute('when', extend=True, prepend=True)
         return when
 
     def evaluate_conditional(self, templar, all_vars):
@@ -130,5 +130,5 @@ class Conditional:
             elif "is defined" in original:
                 return False
             else:
-                raise AnsibleError("error while evaluating conditional (%s): %s" % (original, e))
+                raise AnsibleUndefinedVariable("error while evaluating conditional (%s): %s" % (original, e))
 
diff --git a/lib/ansible/playbook/task.py b/lib/ansible/playbook/task.py
index 275a59f9e88..503c97f322f 100644
--- a/lib/ansible/playbook/task.py
+++ b/lib/ansible/playbook/task.py
@@ -388,7 +388,7 @@ class Task(Base, Conditional, Taggable, Become):
         if self._parent:
             self._parent.set_loader(loader)
 
-    def _get_parent_attribute(self, attr, extend=False):
+    def _get_parent_attribute(self, attr, extend=False, prepend=False):
         '''
         Generic logic to get the attribute or parent attribute for a task value.
         '''
@@ -399,7 +399,7 @@ class Task(Base, Conditional, Taggable, Become):
             if self._parent and (value is None or extend):
                 parent_value = getattr(self._parent, attr, None)
                 if extend:
-                    value = self._extend_value(value, parent_value)
+                    value = self._extend_value(value, parent_value, prepend)
                 else:
                     value = parent_value
         except KeyError: