diff --git a/requirements.txt b/requirements.txt
index c9c80ea0..be244a75 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -35,7 +35,7 @@ rlp<3
 semantic_version
 transaction>=2.2.1
 typing-extensions<4,>=3.7.4
-z3-solver>=4.8.8.0
+z3-solver<4.12.2.0,>=4.8.8.0
 matplotlib
 pre-commit<2.21.0
 certifi>=2020.06.20