diff --git a/Dockerfile b/Dockerfile
index f2ec156..a1608d4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,7 +4,7 @@ COPY . .
 RUN pip install --upgrade pip && pip install \
     black \
     flake8 \
-    mutmut=2.* \
+    mutmut==2.* \
     mypy \
     pylint \
     pytest \