diff --git a/async_substrate_interface/async_substrate.py b/async_substrate_interface/async_substrate.py
index 94abf59..cc78a0e 100644
--- a/async_substrate_interface/async_substrate.py
+++ b/async_substrate_interface/async_substrate.py
@@ -516,7 +516,7 @@ def __init__(
         # TODO reconnection logic
         self.ws_url = ws_url
         self.ws: Optional["ClientConnection"] = None
-        self.max_subscriptions = max_subscriptions
+        self.max_subscriptions = asyncio.Semaphore(max_subscriptions)
         self.max_connections = max_connections
         self.shutdown_timer = shutdown_timer
         self._received = {}
@@ -631,6 +631,7 @@ async def send(self, payload: dict) -> int:
         # async with self._lock:
         original_id = get_next_id()
         # self._open_subscriptions += 1
+        await self.max_subscriptions.acquire()
         try:
             await self.ws.send(json.dumps({**payload, **{"id": original_id}}))
             return original_id
@@ -649,7 +650,9 @@ async def retrieve(self, item_id: int) -> Optional[dict]:
              retrieved item
         """
         try:
-            return self._received.pop(item_id)
+            item = self._received.pop(item_id)
+            self.max_subscriptions.release()
+            return item
         except KeyError:
             await asyncio.sleep(0.001)
             return None
@@ -876,7 +879,7 @@ async def decode_scale(
         scale_bytes: bytes,
         _attempt=1,
         _retries=3,
-        return_scale_obj=False,
+        return_scale_obj: bool = False,
     ) -> Union[ScaleObj, Any]:
         """
         Helper function to decode arbitrary SCALE-bytes (e.g. 0x02000000) according to given RUST type_string
@@ -2528,13 +2531,13 @@ async def runtime_call(
         Returns:
              ScaleType from the runtime call
         """
-        await self.init_runtime(block_hash=block_hash)
+        runtime = await self.init_runtime(block_hash=block_hash)
 
         if params is None:
             params = {}
 
         try:
-            metadata_v15_value = self.runtime.metadata_v15.value()
+            metadata_v15_value = runtime.metadata_v15.value()
 
             apis = {entry["name"]: entry for entry in metadata_v15_value["apis"]}
             api_entry = apis[api]