diff --git a/langfuse/_client/observe.py b/langfuse/_client/observe.py
index e8786a0e0..8082d07e9 100644
--- a/langfuse/_client/observe.py
+++ b/langfuse/_client/observe.py
@@ -195,7 +195,7 @@ def decorator(func: F) -> F:
                     capture_output=should_capture_output,
                     transform_to_string=transform_to_string,
                 )
-                if asyncio.iscoroutinefunction(func)
+                if inspect.iscoroutinefunction(func)
                 else self._sync_observe(
                     func,
                     name=name,