diff --git a/mypy/util.py b/mypy/util.py
index 4b1b918b92e6..75b3e9101731 100644
--- a/mypy/util.py
+++ b/mypy/util.py
@@ -535,9 +535,7 @@ def hash_digest(data: bytes) -> str:
     accidental collision, but we don't really care about any of the
     cryptographic properties.
     """
-    # Once we drop Python 3.5 support, we should consider using
-    # blake2b, which is faster.
-    return hashlib.sha256(data).hexdigest()
+    return hashlib.sha1(data).hexdigest()
 
 
 def parse_gray_color(cup: bytes) -> str: