diff --git a/tests/extmod/uasyncio_heaplock.py b/tests/extmod/uasyncio_heaplock.py
index 34a51cd37..a6b4a0819 100644
--- a/tests/extmod/uasyncio_heaplock.py
+++ b/tests/extmod/uasyncio_heaplock.py
@@ -1,4 +1,8 @@
-# test that basic scheduling of tasks, and uasyncio.sleep_ms, does not use the heap
+# test that the following do not use the heap:
+# - basic scheduling of tasks
+# - uasyncio.sleep_ms
+# - StreamWriter.write, stream is blocked and data to write is a bytes object
+# - StreamWriter.write, when stream is not blocked
 
 import micropython
 
@@ -22,6 +26,17 @@ except ImportError:
         raise SystemExit
 
 
+class TestStream:
+    def __init__(self, blocked):
+        self.blocked = blocked
+
+    def write(self, data):
+        print("TestStream.write", data)
+        if self.blocked:
+            return None
+        return len(data)
+
+
 async def task(id, n, t):
     for i in range(n):
         print(id, i)
@@ -32,14 +47,27 @@ async def main():
     t1 = asyncio.create_task(task(1, 4, 100))
     t2 = asyncio.create_task(task(2, 2, 250))
 
+    # test scheduling tasks, and calling sleep_ms
     micropython.heap_lock()
-
     print("start")
     await asyncio.sleep_ms(5)
     print("sleep")
     await asyncio.sleep_ms(350)
     print("finish")
+    micropython.heap_unlock()
 
+    # test writing to a stream, when the underlying stream is blocked
+    s = asyncio.StreamWriter(TestStream(True), None)
+    micropython.heap_lock()
+    s.write(b"12")
+    micropython.heap_unlock()
+
+    # test writing to a stream, when the underlying stream is not blocked
+    buf = bytearray(b"56")
+    s = asyncio.StreamWriter(TestStream(False), None)
+    micropython.heap_lock()
+    s.write(b"34")
+    s.write(buf)
     micropython.heap_unlock()
 
 
diff --git a/tests/extmod/uasyncio_heaplock.py.exp b/tests/extmod/uasyncio_heaplock.py.exp
index 68c6366c6..5c7b4e3db 100644
--- a/tests/extmod/uasyncio_heaplock.py.exp
+++ b/tests/extmod/uasyncio_heaplock.py.exp
@@ -7,3 +7,6 @@ sleep
 2 1
 1 3
 finish
+TestStream.write b'12'
+TestStream.write b'34'
+TestStream.write bytearray(b'56')