diff --git a/micropip/wheelinfo.py b/micropip/wheelinfo.py
index c6d255f..f2e5a69 100644
--- a/micropip/wheelinfo.py
+++ b/micropip/wheelinfo.py
@@ -54,6 +54,7 @@ class WheelInfo:
     _dist_info: Path | None = None
 
     def __post_init__(self):
+        assert self.url.startswith("http")
         self._project_name = safe_name(self.name)
 
     @classmethod