diff --git a/changelog/unreleased/kong/pluginsocket-proto-wrong-type.yml b/changelog/unreleased/kong/pluginsocket-proto-wrong-type.yml
new file mode 100644
index 000000000000..01f8f1623996
--- /dev/null
+++ b/changelog/unreleased/kong/pluginsocket-proto-wrong-type.yml
@@ -0,0 +1,3 @@
+message: |
+  Fix an issue where external plugins using the protobuf-based protocol would fail to call the `kong.Service.SetUpstream` method with an error `bad argument #2 to 'encode' (table expected, got boolean)`.
+type: bugfix
diff --git a/kong/include/kong/pluginsocket.proto b/kong/include/kong/pluginsocket.proto
index 0ba20a567ae9..fdc581351a21 100644
--- a/kong/include/kong/pluginsocket.proto
+++ b/kong/include/kong/pluginsocket.proto
@@ -328,7 +328,7 @@ service Kong {
     rpc Router_GetRoute(google.protobuf.Empty) returns (Route);
     rpc Router_GetService(google.protobuf.Empty) returns (Service);
 
-    rpc Service_SetUpstream(String) returns (google.protobuf.Empty);
+    rpc Service_SetUpstream(String) returns (Bool);
     rpc Service_SetTarget(Target) returns (google.protobuf.Empty);
 
     rpc Service_Request_SetScheme(String) returns (google.protobuf.Empty);