diff --git a/starlette/templating.py b/starlette/templating.py
index 5595364b..488d8c65 100644
--- a/starlette/templating.py
+++ b/starlette/templating.py
@@ -49,6 +49,7 @@ class Jinja2Templates:
     """
 
     def __init__(self, directory: str) -> None:
+        assert jinja2 is not None, "jinja2 must be installed to use Jinja2Templates"
         self.env = self.get_env(directory)
 
     def get_env(self, directory: str) -> "jinja2.Environment":