diff --git a/HACKING.rst b/HACKING.rst
index e1bec9e51..49ee011d6 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -14,4 +14,3 @@ Mistral Specific Commandments
 - [M328] Python 3: do not use dict.iteritems.
 - [M329] Python 3: do not use dict.iterkeys.
 - [M330] Python 3: do not use dict.itervalues.
-- [M331] String interpolation should be delayed at logging calls.
diff --git a/mistral/hacking/checks.py b/mistral/hacking/checks.py
index 0e0cbfc0c..78dd691ea 100644
--- a/mistral/hacking/checks.py
+++ b/mistral/hacking/checks.py
@@ -30,9 +30,6 @@ import six
 oslo_namespace_imports_dot = re.compile(r"import[\s]+oslo[.][^\s]+")
 oslo_namespace_imports_from_dot = re.compile(r"from[\s]+oslo[.]")
 oslo_namespace_imports_from_root = re.compile(r"from[\s]+oslo[\s]+import[\s]+")
-log_string_interpolation = re.compile(r".*LOG\.(?:error|warn|warning|info"
-                                      r"|critical|exception|debug)"
-                                      r"\([^,]*%[^,]*[,)]")
 
 
 def no_assert_equal_true_false(logical_line):
@@ -108,27 +105,6 @@ def check_python3_no_itervalues(logical_line):
         yield(0, msg)
 
 
-def check_delayed_string_interpolation(logical_line, filename, noqa):
-    """M331: String interpolation should be delayed at logging calls.
-
-    M331: LOG.debug('Example: %s' % 'bad')
-    Okay: LOG.debug('Example: %s', 'good')
-    """
-    msg = ("M331 String interpolation should be delayed to be "
-           "handled by the logging code, rather than being done "
-           "at the point of the logging call. "
-           "Use ',' instead of '%'.")
-
-    if noqa:
-        return
-
-    if 'mistral/tests/' in filename:
-        return
-
-    if log_string_interpolation.match(logical_line):
-        yield(logical_line.index('%'), msg)
-
-
 class BaseASTChecker(ast.NodeVisitor):
     """Provides a simple framework for writing AST-based checks.
 
@@ -297,4 +273,3 @@ def factory(register):
     register(check_python3_no_iterkeys)
     register(check_python3_no_itervalues)
     register(check_python3_xrange)
-    register(check_delayed_string_interpolation)
diff --git a/mistral/tests/unit/base.py b/mistral/tests/unit/base.py
index e90f67455..cbfdbe38f 100644
--- a/mistral/tests/unit/base.py
+++ b/mistral/tests/unit/base.py
@@ -142,7 +142,7 @@ class BaseTest(base.BaseTestCase):
         found = len(filtered_items)
 
         if found != count:
-            LOG.info("[failed test ctx] items=%s, expected_props=%s" % (str(
+            LOG.info("[failed test ctx] items=%s, expected_props=%s", (str(
                 items), props))
             self.fail("Wrong number of items found [props=%s, "
                       "expected=%s, found=%s]" % (props, count, found))
diff --git a/mistral/tests/unit/hacking/test_checks.py b/mistral/tests/unit/hacking/test_checks.py
index dbf15ea44..76f2efed8 100644
--- a/mistral/tests/unit/hacking/test_checks.py
+++ b/mistral/tests/unit/hacking/test_checks.py
@@ -121,59 +121,6 @@ class BaseLoggingCheckTest(base.BaseTest):
         self.assertEqual(0, len(list(checks.check_python3_no_itervalues(
             "six.itervalues(ob))"))))
 
-    def test_check_delayed_string_interpolation(self):
-        checker = checks.check_delayed_string_interpolation
-        code = """
-               msg_w = _LW('Test string (%s)')
-               msg_i = _LI('Test string (%s)')
-               value = 'test'
-
-               LOG.error(_LE("Test string (%s)") % value)
-               LOG.warning(msg_w % 'test%string')
-               LOG.info(msg_i %
-                        "test%string%info")
-               LOG.critical(
-                   _LC('Test string (%s)') % value,
-                   instance=instance)
-               LOG.exception(_LE(" 'Test quotation %s' \"Test\"") % 'test')
-               LOG.debug(' "Test quotation %s" \'Test\'' % "test")
-               LOG.debug('Tesing %(test)s' %
-                         {'test': ','.join(
-                             ['%s=%s' % (name, value)
-                              for name, value in test.items()])})
-               """
-
-        expected_errors = [(5, 34, 'M331'), (6, 18, 'M331'), (7, 15, 'M331'),
-                           (10, 28, 'M331'), (12, 49, 'M331'),
-                           (13, 40, 'M331'), (14, 28, 'M331')]
-        self._assert_has_errors(code, checker, expected_errors=expected_errors)
-        self._assert_has_no_errors(
-            code, checker, filename='mistral/tests/unit/hacking/test_checks.py'
-        )
-
-        code = """
-               msg_w = _LW('Test string (%s)')
-               msg_i = _LI('Test string (%s)')
-               value = 'test'
-
-               LOG.error(_LE("Test string (%s)"), value)
-               LOG.error(_LE("Test string (%s)") % value) # noqa
-               LOG.warn(_LW('Test string (%s)'),
-                        value)
-               LOG.info(msg_i,
-                        "test%string%info")
-               LOG.critical(
-                   _LC('Test string (%s)'), value,
-                   instance=instance)
-               LOG.exception(_LE(" 'Test quotation %s' \"Test\""), 'test')
-               LOG.debug(' "Test quotation %s" \'Test\'', "test")
-               LOG.debug('Tesing %(test)s',
-                         {'test': ','.join(
-                             ['%s=%s' % (name, value)
-                              for name, value in test.items()])})
-               """
-        self._assert_has_no_errors(code, checker)
-
 
 class TestLoggingWithWarn(BaseLoggingCheckTest):
 
diff --git a/tox.ini b/tox.ini
index 37a6673ee..532a3b009 100644
--- a/tox.ini
+++ b/tox.ini
@@ -79,7 +79,8 @@ show-source = true
 builtins = _
 # [H106] Don't put vim configuration in source files.
 # [H203] Use assertIs(Not)None to check for None.
-enable-extensions = H106,H203
+# [H904] Delay string interpolations at logging calls.
+enable-extensions = H106,H203,H904
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools,scripts
 
 [doc8]