diff --git a/src/c-api.adoc b/src/c-api.adoc
index 850af38..aed70db 100644
--- a/src/c-api.adoc
+++ b/src/c-api.adoc
@@ -837,8 +837,8 @@ struct {
 
 struct {
   unsigned mvendorid;
-  unsigned marchid;
-  unsigned mimpid;
+  unsigned long long marchid;
+  unsigned long long mimpid;
 } __riscv_cpu_model;
 ```