Fixes #6100.

lib/pure/asyncfutures.nim

@@ -263,12 +263,12 @@ proc mget*[T](future: FutureVar[T]): var T =
   ## Future has not been finished.
   result = Future[T](future).value
 
-proc finished*[T](future: Future[T] | FutureVar[T]): bool =
+proc finished*(future: FutureBase | FutureVar): bool =
   ## Determines whether ``future`` has completed.
   ##
   ## ``True`` may indicate an error or a value. Use ``failed`` to distinguish.
-  when future is FutureVar[T]:
-    result = (Future[T](future)).finished
+  when future is FutureVar:
+    result = (FutureBase(future)).finished
   else:
     result = future.finished
 

lib/pure/asyncmacro.nim

@@ -32,6 +32,12 @@ template createCb(retFutureSym, iteratorNameSym,
     try:
       if not nameIterVar.finished:
         var next = nameIterVar()
+        # Continue while the yielded future is already finished.
+        while (not next.isNil) and next.finished:
+          next = nameIterVar()
+          if nameIterVar.finished:
+            break
+
         if next == nil:
           if not retFutureSym.finished:
             let msg = "Async procedure ($1) yielded `nil`, are you await'ing a " &