diff --git a/src/frontend/apiserver/backend/clib.go b/src/frontend/apiserver/backend/clib.go
index cbf902d2..50b1265b 100644
--- a/src/frontend/apiserver/backend/clib.go
+++ b/src/frontend/apiserver/backend/clib.go
@@ -332,9 +332,10 @@ func initIDGen() {
 	C.idgen_ctx_init(&gIDCtx)
 }
 
-// GenerateJobID calls the C idgen() to produce a unique job ID.
-// clusterID and apiserverID identify the originating instance;
-// arraySize=1 for normal jobs, >1 for array jobs.
+// GenerateJobID calls the C idgen() to produce a unique ordinary job ID.
+// clusterID and apiserverID identify the originating instance. arraySize
+// must be 1: idgen() allocates ordinary IDs only and returns -EINVAL for
+// any other size; array IDs come from GenerateArrayJobID.
 func GenerateJobID(clusterID, apiserverID int, arraySize int) (uint64, error) {
 	idCtxOnce.Do(initIDGen)
 	var jobID C.uint64_t