diff --git a/src/promptum/providers/openrouter.py b/src/promptum/providers/openrouter.py
index 4ac4231..f84af27 100644
--- a/src/promptum/providers/openrouter.py
+++ b/src/promptum/providers/openrouter.py
@@ -53,7 +53,7 @@ async def generate(
         retry_config: RetryConfig | None = None,
         **kwargs: Any,
     ) -> tuple[str, Metrics]:
-        if not self._client:
+        if self._client is None:
             raise ProviderNotInitializedError()
 
         config = retry_config or self.default_retry_config