diff --git a/src/isolate/backends/container.py b/src/isolate/backends/container.py
index afa9aea..aeacac6 100644
--- a/src/isolate/backends/container.py
+++ b/src/isolate/backends/container.py
@@ -17,6 +17,7 @@ class ContainerizedPythonEnvironment(BaseEnvironment[Path]):
 
     image: dict[str, Any] = field(default_factory=dict)
     python_version: str | None = None
+    requirements: list[str] = field(default_factory=list)
     tags: list[str] = field(default_factory=list)
 
     @classmethod
@@ -34,7 +35,7 @@ def key(self) -> str:
         # dockerfile_str is always there, but the validation is handled by the
         # controller.
         dockerfile_str = self.image.get("dockerfile_str", "")
-        return sha256_digest_of(dockerfile_str, *sorted(self.tags))
+        return sha256_digest_of(dockerfile_str, *self.requirements, *sorted(self.tags))
 
     def create(self, *, force: bool = False) -> Path:
         return Path(sys.exec_prefix)