Index: Python/ceval.c
===================================================================
--- Python/ceval.c	(revision 67068)
+++ Python/ceval.c	(working copy)
@@ -2337,11 +2447,19 @@
 			/* XXX Not the fastest way to call it... */
 			x = PyObject_CallFunctionObjArgs(exit_func, u, v, w,
 							 NULL);
-			if (x == NULL) {
-				Py_DECREF(exit_func);
+			Py_DECREF(exit_func);
+			if (x == NULL)
 				break; /* Go to error exit */
-			}
-			if (u != Py_None && PyObject_IsTrue(x)) {
+
+			if (u != Py_None)
+				err = PyObject_IsTrue(x);
+			else
+				err = 0;
+
+			if (err < 0)
+				break; /* Go to error exit */
+			else if (err > 0) {
+				err = 0;
 				/* There was an exception and a true return */
 				STACKADJ(-2);
 				Py_INCREF(Py_None);
@@ -2354,7 +2472,6 @@
 				   above. Let END_FINALLY do its thing */
 			}
 			Py_DECREF(x);
-			Py_DECREF(exit_func);
 			PREDICT(END_FINALLY);
 			break;
 		}
Index: Lib/test/test_with.py
===================================================================
--- Lib/test/test_with.py	(revision 67068)
+++ Lib/test/test_with.py	(working copy)
@@ -503,7 +503,38 @@
 
         self.assertRaises(GeneratorExit, shouldThrow)
 
+    def testErrorsInBool(self):
+        # issue4589: __exit__ return code may raise an exception
+        # when looking at its truth value.
+                
+        class cm(object):
+            def __init__(self, bool_conversion):
+                class Bool:
+                    def __nonzero__(self):
+                        return bool_conversion()
+                self.exit_result = Bool()
+            def __enter__(self):
+                return 3
+            def __exit__(self, a, b, c):
+                return self.exit_result
 
+        def trueAsBool():
+            with cm(lambda: True):
+                self.fail("Should NOT see this")
+        trueAsBool()
+
+        def falseAsBool():
+            with cm(lambda: False):
+                self.fail("Should raise")
+        self.assertRaises(AssertionError, falseAsBool)
+
+        def failAsBool():
+            with cm(lambda: 1//0):
+                self.fail("Should NOT see this")
+        self.assertRaises(ZeroDivisionError, failAsBool)
+                
+
+
 class NonLocalFlowControlTestCase(unittest.TestCase):
 
     def testWithBreak(self):