diff --git a/docs/manual.md b/docs/manual.md
index cce20061..0e4a77c0 100644
--- a/docs/manual.md
+++ b/docs/manual.md
@@ -353,6 +353,7 @@ Additionally, if the protection domain provides a protected procedure it must al
     void microkit_notify(microkit_channel ch);
     microkit_msginfo microkit_msginfo_new(uint64_t label, uint16_t count);
     uint64_t microkit_msginfo_get_label(microkit_msginfo msginfo);
+    uint64_t microkit_msginfo_get_count(microkit_msginfo msginfo);
     void microkit_irq_ack(microkit_channel ch);
     void microkit_mr_set(uint8_t mr, uint64_t value);
     uint64_t microkit_mr_get(uint8_t mr);
@@ -421,6 +422,10 @@ The message can be passed to `microkit_ppcall` or returned from `protected`.
 
 Returns the label from a message.
 
+## `uint64_t microkit_msginfo_get_count(microkit_msginfo msginfo)`
+
+Returns the count of message registers in the message.
+
 ## `uint64_t microkit_mr_get(uint8_t mr)`
 
 Get a message register.
diff --git a/libmicrokit/include/microkit.h b/libmicrokit/include/microkit.h
index 1fc6c1a4..4c664f40 100644
--- a/libmicrokit/include/microkit.h
+++ b/libmicrokit/include/microkit.h
@@ -70,6 +70,11 @@ static inline uint64_t microkit_msginfo_get_label(microkit_msginfo msginfo)
     return seL4_MessageInfo_get_label(msginfo);
 }
 
+static inline uint64_t microkit_msginfo_get_count(microkit_msginfo msginfo)
+{
+    return seL4_MessageInfo_get_length(msginfo);
+}
+
 static void microkit_mr_set(uint8_t mr, uint64_t value)
 {
     seL4_SetMR(mr, value);