diff --git a/bugbear.py b/bugbear.py
index 485a8e9..f9605a5 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -524,7 +524,7 @@ def visit_For(self, node):
         self.check_for_b020(node)
         self.check_for_b023(node)
         self.check_for_b031(node)
-        self.check_for_b038(node)
+        self.check_for_b909(node)
         self.generic_visit(node)
 
     def visit_AsyncFor(self, node):
@@ -1574,17 +1574,17 @@ def check(num_args, param_name):
         elif node.func.attr == "split":
             check(2, "maxsplit")
 
-    def check_for_b038(self, node: ast.For):
+    def check_for_b909(self, node: ast.For):
         if isinstance(node.iter, ast.Name):
             name = _to_name_str(node.iter)
         elif isinstance(node.iter, ast.Attribute):
             name = _to_name_str(node.iter)
         else:
             return
-        checker = B038Checker(name)
+        checker = B909Checker(name)
         checker.visit(node.body)
         for mutation in checker.mutations:
-            self.errors.append(B038(mutation.lineno, mutation.col_offset))
+            self.errors.append(B909(mutation.lineno, mutation.col_offset))
 
 
 def compose_call_path(node):
@@ -1597,7 +1597,7 @@ def compose_call_path(node):
         yield node.id
 
 
-class B038Checker(ast.NodeVisitor):
+class B909Checker(ast.NodeVisitor):
     # https://docs.python.org/3/library/stdtypes.html#mutable-sequence-types
     MUTATING_FUNCTIONS = (
         "append",
@@ -2146,12 +2146,22 @@ def visit_Lambda(self, node):
         " statement."
     )
 )
-
-B950 = Error(message="B950 line too long ({} > {} characters)")
-
-B038 = Error(
+B909 = Error(
     message=(
-        "B038 editing a loop's mutable iterable often leads to unexpected results/bugs"
+        "B909 editing a loop's mutable iterable often leads to unexpected results/bugs"
     )
 )
-disabled_by_default = ["B901", "B902", "B903", "B904", "B905", "B906", "B908", "B950"]
+B950 = Error(message="B950 line too long ({} > {} characters)")
+
+
+disabled_by_default = [
+    "B901",
+    "B902",
+    "B903",
+    "B904",
+    "B905",
+    "B906",
+    "B908",
+    "B909",
+    "B950",
+]
diff --git a/tests/b038.py b/tests/b909.py
similarity index 100%
rename from tests/b038.py
rename to tests/b909.py
diff --git a/tests/test_bugbear.py b/tests/test_bugbear.py
index 29bc7d0..8aed9fc 100644
--- a/tests/test_bugbear.py
+++ b/tests/test_bugbear.py
@@ -46,7 +46,6 @@
     B035,
     B036,
     B037,
-    B038,
     B901,
     B902,
     B903,
@@ -55,6 +54,7 @@
     B906,
     B907,
     B908,
+    B909,
     B950,
     BugBearChecker,
     BugBearVisitor,
@@ -969,27 +969,27 @@ def test_selfclean_test_bugbear(self):
         self.assertEqual(proc.stdout, b"")
         self.assertEqual(proc.stderr, b"")
 
-    def test_b038(self):
-        filename = Path(__file__).absolute().parent / "b038.py"
-        mock_options = Namespace(select=[], extend_select=["B038"])
+    def test_b909(self):
+        filename = Path(__file__).absolute().parent / "b909.py"
+        mock_options = Namespace(select=[], extend_select=["B909"])
         bbc = BugBearChecker(filename=str(filename), options=mock_options)
         errors = list(bbc.run())
         print(errors)
         expected = [
-            B038(11, 8),
-            B038(26, 8),
-            B038(27, 8),
-            B038(41, 8),
-            B038(47, 8),
-            B038(56, 8),
-            B038(57, 8),
-            B038(58, 8),
-            B038(59, 8),
-            B038(60, 8),
-            B038(61, 8),
-            B038(62, 8),
-            B038(63, 8),
-            B038(74, 8),
+            B909(11, 8),
+            B909(26, 8),
+            B909(27, 8),
+            B909(41, 8),
+            B909(47, 8),
+            B909(56, 8),
+            B909(57, 8),
+            B909(58, 8),
+            B909(59, 8),
+            B909(60, 8),
+            B909(61, 8),
+            B909(62, 8),
+            B909(63, 8),
+            B909(74, 8),
         ]
         self.assertEqual(errors, self.errors(*expected))