diff --git a/artiq/coredevice/comm_moninj.py b/artiq/coredevice/comm_moninj.py
index 08cbcc779..7154ff615 100644
--- a/artiq/coredevice/comm_moninj.py
+++ b/artiq/coredevice/comm_moninj.py
@@ -74,11 +74,11 @@ class CommMonInj:
                 if not ty:
                     return
                 if ty == b"\x00":
-                    payload = await self._reader.read(9)
+                    payload = await self._reader.readexactly(9)
                     channel, probe, value = struct.unpack(">lbl", payload)
                     self.monitor_cb(channel, probe, value)
                 elif ty == b"\x01":
-                    payload = await self._reader.read(6)
+                    payload = await self._reader.readexactly(6)
                     channel, override, value = struct.unpack(">lbb", payload)
                     self.injection_status_cb(channel, override, value)
                 else: