diff --git a/mypyc/irbuild/ll_builder.py b/mypyc/irbuild/ll_builder.py
index e5d46bf5edd4..af17915ec948 100644
--- a/mypyc/irbuild/ll_builder.py
+++ b/mypyc/irbuild/ll_builder.py
@@ -33,7 +33,8 @@
     is_list_rprimitive, is_tuple_rprimitive, is_dict_rprimitive, is_set_rprimitive, PySetObject,
     none_rprimitive, RTuple, is_bool_rprimitive, is_str_rprimitive, c_int_rprimitive,
     pointer_rprimitive, PyObject, PyListObject, bit_rprimitive, is_bit_rprimitive,
-    object_pointer_rprimitive, c_size_t_rprimitive, dict_rprimitive, bytes_rprimitive
+    object_pointer_rprimitive, c_size_t_rprimitive, dict_rprimitive, bytes_rprimitive,
+    is_bytes_rprimitive
 )
 from mypyc.ir.func_ir import FuncDecl, FuncSignature
 from mypyc.ir.class_ir import ClassIR, all_concrete_classes
@@ -1348,7 +1349,8 @@ def builtin_len(self, val: Value, line: int, use_pyssize_t: bool = False) -> Val
         """
         typ = val.type
         size_value = None
-        if is_list_rprimitive(typ) or is_tuple_rprimitive(typ):
+        if (is_list_rprimitive(typ) or is_tuple_rprimitive(typ)
+                or is_bytes_rprimitive(typ)):
             elem_address = self.add(GetElementPtr(val, PyVarObject, 'ob_size'))
             size_value = self.add(LoadMem(c_pyssize_t_rprimitive, elem_address))
             self.add(KeepAlive([val]))
diff --git a/mypyc/test-data/irbuild-bytes.test b/mypyc/test-data/irbuild-bytes.test
index a0c84014edc0..fdb296edc792 100644
--- a/mypyc/test-data/irbuild-bytes.test
+++ b/mypyc/test-data/irbuild-bytes.test
@@ -62,10 +62,8 @@ L0:
     c = r6
     return 1
 
-
 [case testBytesJoin]
 from typing import List
-
 def f(b: List[bytes]) -> bytes:
     return b" ".join(b)
 [out]
@@ -76,3 +74,20 @@ L0:
     r0 = b' '
     r1 = CPyBytes_Join(r0, b)
     return r1
+
+[case testBytesLen]
+def f(b: bytes) -> int:
+    return len(b)
+[out]
+def f(b):
+    b :: bytes
+    r0 :: ptr
+    r1 :: native_int
+    r2 :: short_int
+L0:
+    r0 = get_element_ptr b ob_size :: PyVarObject
+    r1 = load_mem r0 :: native_int*
+    keep_alive b
+    r2 = r1 << 1
+    return r2
+
diff --git a/mypyc/test-data/run-bytes.test b/mypyc/test-data/run-bytes.test
index fe248834497d..41f838b2f07a 100644
--- a/mypyc/test-data/run-bytes.test
+++ b/mypyc/test-data/run-bytes.test
@@ -75,7 +75,7 @@ def test_len() -> None:
 [case testBytearrayBasics]
 from typing import Any
 
-def test_init() -> None:
+def test_basics() -> None:
     brr1: bytes = bytearray(3)
     assert brr1 == bytearray(b'\x00\x00\x00')
     assert brr1 == b'\x00\x00\x00'
@@ -89,6 +89,8 @@ def test_init() -> None:
     brr4: bytes = bytearray('string', 'utf-8')
     assert brr4 == bytearray(b'string')
     assert brr4 == b'string'
+    assert len(brr1) == 3
+    assert len(brr2) == 4
 
 def f(b: bytes) -> bool:
     return True