diff --git a/tinygrad/ops.py b/tinygrad/ops.py
index ca6a9068..08075e44 100644
--- a/tinygrad/ops.py
+++ b/tinygrad/ops.py
@@ -1,8 +1,7 @@
 from __future__ import annotations
-from typing import Any, List, Optional, Set, Union, Tuple, Dict, Callable, cast, TYPE_CHECKING, TypeVar, DefaultDict
+from typing import Any, List, Optional, Set, Union, Tuple, Dict, Callable, cast, TYPE_CHECKING, TypeVar
 import sys, time, functools, itertools, math, operator, hashlib
 from enum import auto, IntEnum, Enum
-from collections import defaultdict
 from dataclasses import dataclass, field
 from tinygrad.dtype import ConstType, ImageDType, PtrDType, dtypes, DType, truncate
 from tinygrad.helpers import _CURRENT_KERNEL, ContextVar, pretty_print, prod, getenv, all_same
@@ -466,18 +465,19 @@ class UPatAny(UPat):
 class PatternMatcher:
   def __init__(self, patterns:List[Tuple[UPat, Callable]]):
     self.patterns = patterns
-    self.pdict: DefaultDict[Tuple[UOps, Any], List[Tuple[UPat, Callable, Set]]] = defaultdict(list)
+    # NOTE: use of DefaultDict here is very dangerous! all keys will live for the lifetime of the PatternMatcher!
+    self.pdict: Dict[Tuple[UOps, Any], List[Tuple[UPat, Callable, Set]]] = {}
     # uop is required, arg is optional
     for p,fxn in self.patterns:
       assert p.op is not None
-      for uop in p.op: self.pdict[(uop, p.arg)].append((p, fxn, p.early_reject))
+      for uop in p.op: self.pdict.setdefault((uop, p.arg), []).append((p, fxn, p.early_reject))
 
   @functools.lru_cache(None)  # pylint: disable=method-cache-max-size-none
   def __add__(self, more:PatternMatcher): return PatternMatcher(self.patterns+more.patterns)
 
   def rewrite(self, uop:UOp, ctx=None) -> Optional[UOp]:
     ler = set([v for u in uop.src for v in ((u.op, u.arg), (u.op, None))])
-    for p,fxn,early_reject in self.pdict[(uop.op, uop.arg)] + ([] if uop.arg is None else self.pdict[(uop.op, None)]):
+    for p,fxn,early_reject in self.pdict.get((uop.op, uop.arg), []) + ([] if uop.arg is None else self.pdict.get((uop.op, None), [])):
       if not early_reject.issubset(ler): continue
       if (matches := p.match(uop, {})) and (ret:=(fxn(ctx, **matches[0]) if ctx is not None else fxn(**matches[0]))) is not None: return ret
     return None
@@ -502,7 +502,7 @@ class TrackedPatternMatcher(PatternMatcher):
   def rewrite(self, uop:UOp, ctx=None) -> Optional[UOp]:
     ret = None
     ler = set([v for u in uop.src for v in ((u.op, u.arg), (u.op, None))])
-    for p,fxn,early_reject in self.pdict[(uop.op, uop.arg)] + ([] if uop.arg is None else self.pdict[(uop.op, None)]):
+    for p,fxn,early_reject in self.pdict.get((uop.op, uop.arg), []) + ([] if uop.arg is None else self.pdict.get((uop.op, None), [])):
       st = time.perf_counter()
       if not early_reject.issubset(ler):
         match_stats[p][2] += time.perf_counter()-st