--- a/genshi/template.py
+++ b/genshi/template.py
@@ -681,14 +681,18 @@
                                        self.filename, *stream.next()[2][1:])
         if matched:
             return []
-        if not self.expr:
-            raise TemplateRuntimeError('"when" directive has no test condition',
+        if not self.expr and '_choose.value' not in frame:
+            raise TemplateRuntimeError('either "choose" or "when" directive '
+                                       'must have a test expression',
                                        self.filename, *stream.next()[2][1:])
-        value = self.expr.evaluate(ctxt)
         if '_choose.value' in frame:
-            matched = (value == frame['_choose.value'])
+            value = frame['_choose.value']
+            if self.expr:
+                matched = value == self.expr.evaluate(ctxt)
+            else:
+                matched = bool(value)
         else:
-            matched = bool(value)
+            matched = bool(self.expr.evaluate(ctxt))
         frame['_choose.matched'] = matched
         if not matched:
             return []

--- a/genshi/tests/template.py
+++ b/genshi/tests/template.py
@@ -198,6 +198,21 @@
         </doc>""")
         self.assertRaises(TemplateRuntimeError, str, tmpl.generate())
 
+    def test_when_without_test_but_with_choose_value(self):
+        """
+        Verify that an `when` directive that doesn't have a `test` attribute
+        works as expected as long as the parent `choose` directive has a test
+        expression.
+        """
+        tmpl = MarkupTemplate("""<doc xmlns:py="http://genshi.edgewall.org/">
+          <div py:choose="foo" py:strip="">
+            <py:when>foo</py:when>
+          </div>
+        </doc>""")
+        self.assertEqual("""<doc>
+            foo
+        </doc>""", str(tmpl.generate(foo='Yeah')))
+
     def test_otherwise_without_test(self):
         """
         Verify that an `otherwise` directive can be used without a `test`