diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index a3c2cd12277..1a4cc5e5d97 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -89,7 +89,8 @@ struct ProcSignalHeader
 /*
  * We reserve a slot for each possible ProcNumber, plus one for each
  * possible auxiliary process type.  (This scheme assumes there is not
- * more than one of any auxiliary process type at a time.)
+ * more than one of any auxiliary process type at a time, except for
+ * IO workers.)
  */
 #define NumProcSignalSlots	(MaxBackends + NUM_AUXILIARY_PROCS)
 
diff --git a/src/backend/storage/ipc/sinvaladt.c b/src/backend/storage/ipc/sinvaladt.c
index 2da91738c32..c5748b690f4 100644
--- a/src/backend/storage/ipc/sinvaladt.c
+++ b/src/backend/storage/ipc/sinvaladt.c
@@ -198,7 +198,8 @@ typedef struct SISeg
 /*
  * We reserve a slot for each possible ProcNumber, plus one for each
  * possible auxiliary process type.  (This scheme assumes there is not
- * more than one of any auxiliary process type at a time.)
+ * more than one of any auxiliary process type at a time, except for
+ * IO workers.)
  */
 #define NumProcStateSlots	(MaxBackends + NUM_AUXILIARY_PROCS)
 
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 72f5655fb34..629772b0381 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -353,7 +353,7 @@ typedef enum BackendType
 	 * Auxiliary processes. These have PGPROC entries, but they are not
 	 * attached to any particular database, and cannot run transactions or
 	 * even take heavyweight locks. There can be only one of each of these
-	 * running at a time.
+	 * running at a time, except for IO workers.
 	 *
 	 * If you modify these, make sure to update NUM_AUXILIARY_PROCS and the
 	 * glossary in the docs.