diff --git a/pyproject.toml b/pyproject.toml
index 27c8fd9..6d8e8dd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -37,6 +37,7 @@ dynamic = ["version"]
 test = [
     "scipy < 2",
     "coverage < 8",
+    "emcee < 4",
 ]
 dev = [
     "pre-commit",