diff --git a/src/hostcalls.rs b/src/hostcalls.rs
index 7c8d4da6..1ba04b37 100644
--- a/src/hostcalls.rs
+++ b/src/hostcalls.rs
@@ -793,7 +793,7 @@ extern "C" {
 }
 
 pub fn dispatch_grpc_call(
-    upstream_name: &str,
+    upstream: &[u8],
     service_name: &str,
     method_name: &str,
     initial_metadata: Vec<(&str, &[u8])>,
@@ -804,8 +804,8 @@ pub fn dispatch_grpc_call(
     let serialized_initial_metadata = utils::serialize_map_bytes(initial_metadata);
     unsafe {
         match proxy_grpc_call(
-            upstream_name.as_ptr(),
-            upstream_name.len(),
+            upstream.as_ptr(),
+            upstream.len(),
             service_name.as_ptr(),
             service_name.len(),
             method_name.as_ptr(),
diff --git a/src/traits.rs b/src/traits.rs
index 819008c0..10747c27 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -116,7 +116,7 @@ pub trait Context {
 
     fn dispatch_grpc_call(
         &self,
-        upstream_name: &str,
+        upstream: &[u8],
         service_name: &str,
         method_name: &str,
         initial_metadata: Vec<(&str, &[u8])>,
@@ -124,7 +124,7 @@ pub trait Context {
         timeout: Duration,
     ) -> Result<u32, Status> {
         hostcalls::dispatch_grpc_call(
-            upstream_name,
+            upstream,
             service_name,
             method_name,
             initial_metadata,