diff --git a/inc/hf/api.h b/inc/hf/api.h
index 21bed0c..7d6b7c0 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -24,7 +24,7 @@
 
 void api_init(struct mpool *ppool);
 spci_vm_id_t api_vm_get_id(const struct vcpu *current);
-int64_t api_vm_get_count(void);
+spci_vm_count_t api_vm_get_count(void);
 int64_t api_vcpu_get_count(spci_vm_id_t vm_id, const struct vcpu *current);
 void api_regs_state_saved(struct vcpu *vcpu);
 struct hf_vcpu_run_return api_vcpu_run(spci_vm_id_t vm_id, uint32_t vcpu_idx,
diff --git a/inc/hf/vm.h b/inc/hf/vm.h
index 6a8f8b1..4bebc20 100644
--- a/inc/hf/vm.h
+++ b/inc/hf/vm.h
@@ -98,7 +98,7 @@
 };
 
 bool vm_init(uint32_t vcpu_count, struct mpool *ppool, struct vm **new_vm);
-uint32_t vm_get_count(void);
+spci_vm_count_t vm_get_count(void);
 struct vm *vm_find(spci_vm_id_t id);
 struct vm_locked vm_lock(struct vm *vm);
 void vm_unlock(struct vm_locked *locked);
diff --git a/inc/vmapi/hf/call.h b/inc/vmapi/hf/call.h
index 239244f..01be71f 100644
--- a/inc/vmapi/hf/call.h
+++ b/inc/vmapi/hf/call.h
@@ -56,7 +56,7 @@
 /**
  * Returns the number of secondary VMs.
  */
-static inline int64_t hf_vm_get_count(void)
+static inline spci_vm_count_t hf_vm_get_count(void)
 {
 	return hf_call(HF_VM_GET_COUNT, 0, 0, 0);
 }
diff --git a/inc/vmapi/hf/spci.h b/inc/vmapi/hf/spci.h
index 523c4ae..c387e62 100644
--- a/inc/vmapi/hf/spci.h
+++ b/inc/vmapi/hf/spci.h
@@ -60,8 +60,15 @@
 
 /* clang-format on */
 
+/** The ID of a VM. These are assigned sequentially. */
 typedef uint16_t spci_vm_id_t;
 
+/**
+ * A count of VMs. This has the same range as the VM IDs but we give it a
+ * different name to make the different semantics clear.
+ */
+typedef spci_vm_id_t spci_vm_count_t;
+
 /** SPCI common message header. */
 struct spci_message {
 	/*
diff --git a/src/api.c b/src/api.c
index 698e788..ccbeeda 100644
--- a/src/api.c
+++ b/src/api.c
@@ -216,7 +216,7 @@
 /**
  * Returns the number of VMs configured to run.
  */
-int64_t api_vm_get_count(void)
+spci_vm_count_t api_vm_get_count(void)
 {
 	return vm_get_count();
 }
diff --git a/src/vm.c b/src/vm.c
index e9919d8..8532144 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -23,7 +23,7 @@
 #include "vmapi/hf/call.h"
 
 static struct vm vms[MAX_VMS];
-static uint32_t vm_count;
+static spci_vm_count_t vm_count;
 
 bool vm_init(uint32_t vcpu_count, struct mpool *ppool, struct vm **new_vm)
 {
@@ -69,7 +69,7 @@
 	return true;
 }
 
-uint32_t vm_get_count(void)
+spci_vm_count_t vm_get_count(void)
 {
 	return vm_count;
 }