diff --git a/py/_code/_assertionnew.py b/py/_code/_assertionnew.py
index a80ae898c..192eecfce 100644
--- a/py/_code/_assertionnew.py
+++ b/py/_code/_assertionnew.py
@@ -108,10 +108,16 @@ unary_map = {
 
 
 class DebugInterpreter(ast.NodeVisitor):
-    """Interpret AST nodes to gleam useful debugging information."""
+    """Interpret AST nodes to gleam useful debugging information.
+
+    The _pytesthook attribute is used to detect if the py.test
+    pytest_assertion plugin is loaded and if so call it's hooks.
+    """
 
     def __init__(self, frame):
         self.frame = frame
+        self._pytesthook = getattr(py.builtin.builtins.AssertionError,
+                                   "_pytesthook")
 
     def generic_visit(self, node):
         # Fallback when we don't have a special implementation.
@@ -177,13 +183,14 @@ class DebugInterpreter(ast.NodeVisitor):
             if not result:
                 break
             left_explanation, left_result = next_explanation, next_result
-        hook_result = py.test.config.hook.pytest_assert_compare(
-            op=op_symbol, left=left_result, right=next_result)
-        if hook_result:
-            for new_expl in hook_result:
-                if new_expl:
-                    explanation = '\n~'.join(new_expl)
-                    break
+        if self._pytesthook:
+            hook_result = self._pytesthook.pytest_assert_compare(
+                op=op_symbol, left=left_result, right=next_result)
+            if hook_result:
+                for new_expl in hook_result:
+                    if new_expl:
+                        explanation = '\n~'.join(new_expl)
+                        break
         return explanation, result
 
     def visit_BoolOp(self, boolop):
diff --git a/py/_plugin/pytest_assertion.py b/py/_plugin/pytest_assertion.py
index 8f2aa5b22..2816671ab 100644
--- a/py/_plugin/pytest_assertion.py
+++ b/py/_plugin/pytest_assertion.py
@@ -8,10 +8,15 @@ def pytest_addoption(parser):
         help="disable python assert expression reinterpretation."),
 
 def pytest_configure(config):
+    # The _pytesthook attribute on the AssertionError is used by
+    # py._code._assertionnew to detect this plugin was loaded and in
+    # turn call the hooks defined here as part of the
+    # DebugInterpreter.
     if not config.getvalue("noassert") and not config.getvalue("nomagic"):
         warn_about_missing_assertion()
         config._oldassertion = py.builtin.builtins.AssertionError
         py.builtin.builtins.AssertionError = py.code._AssertionError
+        py.builtin.builtins.AssertionError._pytesthook = config.hook
 
 def pytest_unconfigure(config):
     if hasattr(config, '_oldassertion'):