diff --git a/inc/vmapi/hf/call.h b/inc/vmapi/hf/call.h
index 64e658f..3ba985c 100644
--- a/inc/vmapi/hf/call.h
+++ b/inc/vmapi/hf/call.h
@@ -125,8 +125,6 @@
  * Called by secondary VMs to receive a message. The call can optionally block
  * until a message is received.
  *
- * If no message was received, the VM ID will be HF_INVALID_VM_ID.
- *
  * The mailbox must be cleared before a new message can be received.
  *
  * If no message is immediately available, `block` is true, and there are no
@@ -135,6 +133,12 @@
  * enabled interrupt becomes pending. This matches the behaviour of the WFI
  * instruction on aarch64, except that a message becoming available is also
  * treated like a wake-up event.
+ *
+ * Returns:
+ *  - SPCI_SUCCESS if a message is successfully received.
+ *  - SPCI_INTERRUPTED if the caller is the primary VM or an interrupt happened
+ *    during the call.
+ *  - SPCI_RETRY if there was no pending message, and `block` was false.
  */
 static inline int32_t spci_msg_recv(int32_t attributes)
 {
diff --git a/inc/vmapi/hf/types.h b/inc/vmapi/hf/types.h
index f4f9998..0479012 100644
--- a/inc/vmapi/hf/types.h
+++ b/inc/vmapi/hf/types.h
@@ -36,9 +36,6 @@
 /** The ID of the primary VM which is responsible for scheduling. */
 #define HF_PRIMARY_VM_ID 0
 
-/* Invalid values for fields to indicate absence or errors. */
-#define HF_INVALID_VM_ID 0xffffffff
-
 /* Sleep value for an indefinite period of time. */
 #define HF_SLEEP_INDEFINITE 0xffffffffffffff