Index: src/org/python/core/Py.java
===================================================================
--- src/org/python/core/Py.java	(revision 3416)
+++ src/org/python/core/Py.java	(working copy)
@@ -1915,8 +1915,15 @@
         }
         return false;
     }
-        
+
+	private static int get_recursionlimit() {
+		return Py.getSystemState().getrecursionlimit();
+	}
+
+    public static int recursion_depth=1000;
+
     public static boolean isInstance(PyObject obj, PyObject cls) {
+		recursion_depth--;
         if (cls instanceof PyType) {
             PyType objtype = obj.getType();
             if (objtype == cls)
@@ -1928,9 +1935,14 @@
             return ((PyClass) obj.fastGetClass()).isSubClass((PyClass) cls);
         } else if (cls.getClass() == PyTuple.class) {
             for (int i = 0; i < cls.__len__(); i++) {
-                if (isInstance(obj, cls.__getitem__(i)))
+				if(recursion_depth == 0)
+					throw Py.RuntimeError("nest level of tuple too deep");
+                if (isInstance(obj, cls.__getitem__(i))) {
+					recursion_depth = get_recursionlimit();
                     return true;
+				}	
             }
+			recursion_depth = get_recursionlimit();
             return false;
         } else {
             if (cls.__findattr__("__bases__") == null)
@@ -1943,8 +1955,10 @@
             return abstract_issubclass(ocls, cls);
         }
     }
+	
     
     public static boolean isSubClass(PyObject derived,PyObject cls) {
+		recursion_depth--;
         if (derived instanceof PyType && cls instanceof PyType) {
             if (derived == cls) return true;
             return ((PyType)derived).isSubType((PyType)cls);
@@ -1952,9 +1966,14 @@
             return ((PyClass)derived).isSubClass((PyClass)cls);            
         } else if (cls.getClass() == PyTuple.class) {
             for (int i = 0; i < cls.__len__(); i++) {
-                if (isSubClass(derived, cls.__getitem__(i)))
+				if(recursion_depth == 0)
+					throw Py.RuntimeError("nest level of tuple too deep");
+                if (isSubClass(derived, cls.__getitem__(i))) {
+					recursion_depth = get_recursionlimit();
                     return true;
+				}	
             }
+			recursion_depth = get_recursionlimit();
             return false;
         } else {
             if (derived.__findattr__("__bases__") == null)

Index: Lib/test/test_isinstance.py
===================================================================
--- Lib/test/test_isinstance.py	(revision 3416)
+++ Lib/test/test_isinstance.py	(working copy)
@@ -268,16 +268,18 @@
 
 def test_main():
     if test_support.is_jython:
-# Jython transition 2.3
-# isinstance and issubclass don't prevent a StackOverflow with a deeply nested tuple 
-# http://jython.org/bugs/1768988
-        del TestIsInstanceIsSubclass.test_isinstance_recursion_limit
-        del TestIsInstanceIsSubclass.test_subclass_recursion_limit
+	TestIsInstanceIsSubclass.test_isinstance_recursion_limit
+	TestIsInstanceIsSubclass.test_subclass_recursion_limit
+	test_support.run_unittest(
+		TestIsSubclassExceptions
+	)
+	test_support.run_unittest(
+		TestIsInstanceIsSubclass
+	)
     test_support.run_unittest(
-        TestIsInstanceExceptions,
-        TestIsSubclassExceptions,
-        TestIsInstanceIsSubclass
+        TestIsInstanceExceptions
     )
+	
 
 
 if __name__ == '__main__':