diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index f35626df1dea062d8d7b7c35858efd9a4f42c05f..2e6e61bbe81b39646ea63047792c2c172badb4bf 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -1184,7 +1184,7 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,
 
 	asm volatile("vmcall"
 		     : "=a"(r)
-		     : "b"(a0), "c"(a1), "d"(a2), "S"(a3));
+		     : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
 	return r;
 }