diff --git a/taskflow/tests/unit/test_flattening.py b/taskflow/tests/unit/test_flattening.py
index e4f112a9..46b66272 100644
--- a/taskflow/tests/unit/test_flattening.py
+++ b/taskflow/tests/unit/test_flattening.py
@@ -20,6 +20,7 @@ import string
 
 import networkx as nx
 
+from taskflow import exceptions as exc
 from taskflow.patterns import graph_flow as gf
 from taskflow.patterns import linear_flow as lf
 from taskflow.patterns import unordered_flow as uf
@@ -167,3 +168,20 @@ class FlattenTest(test.TestCase):
                           set(g_utils.get_no_predecessors(g)))
         self.assertEquals(set([d]),
                           set(g_utils.get_no_successors(g)))
+
+    def test_flatten_checks_for_dups(self):
+        flo = gf.Flow("test").add(
+            t_utils.DummyTask(name="a"),
+            t_utils.DummyTask(name="a")
+        )
+        with self.assertRaisesRegexp(exc.InvariantViolationException,
+                                     '^Tasks with duplicate names'):
+            f_utils.flatten(flo)
+
+    def test_flatten_checks_for_dups_globally(self):
+        flo = gf.Flow("test").add(
+            gf.Flow("int1").add(t_utils.DummyTask(name="a")),
+            gf.Flow("int2").add(t_utils.DummyTask(name="a")))
+        with self.assertRaisesRegexp(exc.InvariantViolationException,
+                                     '^Tasks with duplicate names'):
+            f_utils.flatten(flo)
diff --git a/taskflow/utils/flow_utils.py b/taskflow/utils/flow_utils.py
index 18bab12a..c38ce32c 100644
--- a/taskflow/utils/flow_utils.py
+++ b/taskflow/utils/flow_utils.py
@@ -18,11 +18,13 @@
 
 import networkx as nx
 
+from taskflow import exceptions
 from taskflow.patterns import graph_flow as gf
 from taskflow.patterns import linear_flow as lf
 from taskflow.patterns import unordered_flow as uf
 from taskflow import task
 from taskflow.utils import graph_utils as gu
+from taskflow.utils import misc
 
 
 # Use the 'flatten' reason as the need to add an edge here, which is useful for
@@ -110,6 +112,14 @@ def _flatten(item, flattened):
 
 def flatten(item, freeze=True):
     graph = _flatten(item, set())
+
+    dup_names = misc.get_duplicate_keys(graph.nodes_iter(),
+                                        key=lambda node: node.name)
+    if dup_names:
+        raise exceptions.InvariantViolationException(
+            "Tasks with duplicate names found: %s"
+            % ', '.join(sorted(dup_names)))
+
     if freeze:
         # Frozen graph can't be modified...
         return nx.freeze(graph)
diff --git a/taskflow/utils/misc.py b/taskflow/utils/misc.py
index fc076d12..df27edb3 100644
--- a/taskflow/utils/misc.py
+++ b/taskflow/utils/misc.py
@@ -22,6 +22,7 @@ from distutils import version
 import collections
 import copy
 import errno
+import itertools
 import logging
 import os
 import sys
@@ -51,6 +52,18 @@ def get_version_string(obj):
     return obj_version
 
 
+def get_duplicate_keys(iterable, key=None):
+    if key is not None:
+        iterable = itertools.imap(key, iterable)
+    keys = set()
+    duplicates = set()
+    for item in iterable:
+        if item in keys:
+            duplicates.add(item)
+        keys.add(item)
+    return duplicates
+
+
 class ExponentialBackoff(object):
     def __init__(self, attempts, exponent=2):
         self.attempts = int(attempts)