diff --git a/test/test_jit.py b/test/test_jit.py
index a97dd5a589..3a9e1f04d4 100644
--- a/test/test_jit.py
+++ b/test/test_jit.py
@@ -15,6 +15,25 @@ class TestJit(unittest.TestCase):
       c = add(a, b)
       np.testing.assert_equal(c.numpy(), a.numpy()+b.numpy())
 
+  def test_jit_shape_mismatch(self):
+    @TinyJit
+    def add(a, b): return (a+b).realize()
+    for _ in range(3):
+      a = Tensor.randn(10, 10)
+      b = Tensor.randn(10, 10)
+      c = add(a, b)
+    bad = Tensor.randn(20, 20)
+    with self.assertRaises(AssertionError):
+      add(a, bad)
+
+  def test_jit_duplicate_fail(self):
+    # the jit doesn't support duplicate arguments
+    @TinyJit
+    def add(a, b): return (a+b).realize()
+    a = Tensor.randn(10, 10)
+    with self.assertRaises(AssertionError):
+      add(a, a)
+
   def test_kwargs_jit(self):
     @TinyJit
     def add_kwargs(first, second): return (first+second).realize()
diff --git a/tinygrad/jit.py b/tinygrad/jit.py
index c22b8845dc..72e08b7ed2 100644
--- a/tinygrad/jit.py
+++ b/tinygrad/jit.py
@@ -1,6 +1,6 @@
 from typing import Callable, List, Tuple, Any, Dict, cast, Union
 import functools, itertools
-from tinygrad.helpers import DEBUG
+from tinygrad.helpers import DEBUG, DType
 
 from tinygrad.lazy import Device
 from tinygrad.tensor import Tensor
@@ -12,7 +12,7 @@ class TinyJit:
     self.cnt: int = 0
     self.jit_cache: List[Tuple[Callable, Any]] = []  # TODO: Any should be List[RawBuffer], but this fails
     self.ret: Any = None
-    self.input_replace: Dict[Tuple[int, int], Union[int, str]]= {}
+    self.input_replace: Dict[Tuple[int, int], Tuple[Union[int, str], int, DType]]= {}   # (kernel_number, buffer_number) -> (input_name, expected_size, expected_type)
 
   # add support for instance methods
   def __get__(self, obj, objtype): return functools.partial(self.__call__, obj)
@@ -22,10 +22,13 @@ class TinyJit:
     # NOTE: this cast is needed since although we know realize will create a ".realized" DeviceBuffer, the type checker doesn't
     input_rawbuffers: Dict[Union[int, str], RawBuffer] = {cast(Union[int, str], k):cast(RawBuffer, v.realize().lazydata.realized) for k,v in itertools.chain(enumerate(args), kwargs.items()) if isinstance(v, Tensor)}
     assert len(input_rawbuffers) != 0, "no inputs to JIT"
+    assert set(input_rawbuffers.values()) == len(input_rawbuffers), "duplicate inputs to JIT"
     if self.cnt >= 2:
-      for (j,i),idx in self.input_replace.items(): self.jit_cache[j][1][i] = input_rawbuffers[idx]
+      for (j,i),(input_name, expected_size, expected_type) in self.input_replace.items():
+        assert input_rawbuffers[input_name].size == expected_size and input_rawbuffers[input_name].dtype == expected_type, f"size or type mismatch in JIT, {input_rawbuffers[input_name]} != <{expected_size}, {expected_type}>"
+        self.jit_cache[j][1][i] = input_rawbuffers[input_name]
       for prg, args in self.jit_cache: prg(args, jit=True)
-      for (j,i),idx in self.input_replace.items(): self.jit_cache[j][1][i] = None
+      for (j,i) in self.input_replace.keys(): self.jit_cache[j][1][i] = None
     elif self.cnt == 1:
       GlobalCounters.cache = []
       self.ret = self.fxn(*args, **kwargs)
@@ -38,10 +41,10 @@ class TinyJit:
       for j,(prg,args) in enumerate(self.jit_cache):  # pylint: disable=E1133
         for i,a in enumerate(args):
           if a in input_rawbuffers.values():
-            self.input_replace[(j,i)] = [k for k,v in input_rawbuffers.items() if v == a][0]
+            self.input_replace[(j,i)] = [(k, v.size, v.dtype) for k,v in input_rawbuffers.items() if v == a][0]
         #if prg.local_size is None: prg.local_size = prg.optimize_local_size(args, preserve_output=True)  # the JIT can optimize local
-      assert set(self.input_replace.values()) == set(input_rawbuffers.keys()), "some input tensors not found"
-      for (j,i),idx in self.input_replace.items(): self.jit_cache[j][1][i] = None
+      assert set([x[0] for x in self.input_replace.values()]) == set(input_rawbuffers.keys()), "some input tensors not found"
+      for (j,i) in self.input_replace.keys(): self.jit_cache[j][1][i] = None
     elif self.cnt == 0:
       self.ret = self.fxn(*args, **kwargs)
     self.cnt += 1