diff --git a/rust/src/event.rs b/rust/src/event.rs
index 72afd3cf6..156968a69 100644
--- a/rust/src/event.rs
+++ b/rust/src/event.rs
@@ -29,7 +29,7 @@ type GuestfsEventCallback = extern "C" fn(
     u64,
     i32,
     i32,
-    *const i8,
+    *const c_char,
     usize,
     *const u64,
     usize,