diff --git a/lib/api/src/sys/externals/function.rs b/lib/api/src/sys/externals/function.rs
index 1b90a43c462..8392e9b4203 100644
--- a/lib/api/src/sys/externals/function.rs
+++ b/lib/api/src/sys/externals/function.rs
@@ -1105,7 +1105,7 @@ mod inner {
     /// the trait system to automatically generate the appropriate
     /// host functions.
     #[doc(hidden)]
-    pub trait HostFunctionKind {}
+    pub trait HostFunctionKind: private::HostFunctionKindSealed {}
 
     /// An empty struct to help Rust typing to determine
     /// when a `HostFunction` does have an environment.