diff --git a/faststreams/input_stream.nim b/faststreams/input_stream.nim
index 20c292a..7894576 100644
--- a/faststreams/input_stream.nim
+++ b/faststreams/input_stream.nim
@@ -6,7 +6,7 @@ const
   debugHelpers = false
 
 type
-  StreamReader = proc (bufferStart: ptr byte, bufferSize: int): int
+  StreamReader = proc (bufferStart: ptr byte, bufferSize: int): int {.gcsafe.}
   # TODO: use openarray once it's supported
   AsyncStreamReader = StreamReader # proc (bufferStart: ptr byte, bufferSize: int): Future[int]
   CloseStreamProc = proc ()