diff --git a/mypyc/genops.py b/mypyc/genops.py
index 2fc611c1c925..ec5226d6966e 100644
--- a/mypyc/genops.py
+++ b/mypyc/genops.py
@@ -519,7 +519,14 @@ def visit_call_expr(self, expr: CallExpr) -> int:
         if fn == 'len' and len(expr.args) == 1 and expr.arg_kinds == [ARG_POS]:
             target = self.alloc_target(RTType('int'))
             arg = self.accept(expr.args[0])
-            self.add(PrimitiveOp(target, PrimitiveOp.LIST_LEN, arg))
+
+            expr_rttype = type_to_rttype(self.types[expr.args[0]])
+            if expr_rttype.name == 'list':
+                self.add(PrimitiveOp(target, PrimitiveOp.LIST_LEN, arg))
+            elif isinstance(expr_rttype, TupleRTType):
+                self.add(LoadInt(target, len(expr_rttype.types)))
+            else:
+                assert False, "unsupported use of len"
         else:
             target = self.alloc_target(RTType('int'))
             args = [self.accept(arg) for arg in expr.args]
diff --git a/test-data/fixtures/ir.py b/test-data/fixtures/ir.py
index 4c81f24a880a..2ace4dcfcee9 100644
--- a/test-data/fixtures/ir.py
+++ b/test-data/fixtures/ir.py
@@ -1,7 +1,7 @@
 # These builtins stubs are used implicitly in AST to IR generation
 # test cases.
 
-from typing import TypeVar, Generic, List, Iterator, Iterable
+from typing import TypeVar, Generic, List, Iterator, Iterable, Sized
 
 T = TypeVar('T')
 
@@ -33,14 +33,15 @@ class bool: pass
 class tuple: pass
 class function: pass
 
-class list(Generic[T], Iterable[T]):
+class list(Generic[T], Iterable[T], Sized):
     def __getitem__(self, i: int) -> T: pass
     def __setitem__(self, i: int, o: T) -> None: pass
     def __mul__(self, i: int) -> List[T]: pass
     def __rmul__(self, i: int) -> List[T]: pass
     def __iter__(self) -> Iterator[T]: pass
+    def __len__(self) -> int: pass
     def append(self, x: T) -> None: pass
 
-def len(o: list) -> int: pass
+def len(o: Sized) -> int: pass
 def print(*object) -> None: pass
 def range(x: int) -> Iterator[int]: pass
diff --git a/test-data/genops-basic.test b/test-data/genops-basic.test
index 22b0634e4d75..37752116ea4d 100644
--- a/test-data/genops-basic.test
+++ b/test-data/genops-basic.test
@@ -450,3 +450,15 @@ L0:
     t = (r0, r1)
     r2 = t[1]
     return r2
+
+[case testTupleLen]
+from typing import Tuple
+def f(x: Tuple[bool, bool, int]) -> int:
+    return len(x)
+[out]
+def f(x):
+    x :: tuple
+    r0 :: int
+L0:
+    r0 = 3
+    return r0