diff --git a/setup.py b/setup.py
index 79ed337..f3b8ef1 100644
--- a/setup.py
+++ b/setup.py
@@ -43,7 +43,7 @@
     packages=find_namespace_packages(include=["pytket.*"]),
     include_package_data=True,
     install_requires=[
-        "pytket >= 1.39.0",
+        "pytket >= 1.39.0, < 2",
         "networkx >= 2.8.8",
     ],
     classifiers=[