diff --git a/cmdline/dry.c b/cmdline/dry.c
index 1f098e23..f83212ee 100644
--- a/cmdline/dry.c
+++ b/cmdline/dry.c
@@ -191,7 +191,9 @@ static int state_dry_process(struct snapraid_state* state, struct snapraid_parit
 	/* initialize the io threads */
 	io_init(&io, state, state->opt.io_cache, buffermax, dry_data_reader, handle, diskmax, dry_parity_reader, 0, parity_handle, state->level);
 
-	waiting_map = malloc_nofail((diskmax + RAID_PARITY_MAX) * sizeof(unsigned));
+	/* possibly waiting disks */
+	waiting_mac = diskmax > RAID_PARITY_MAX ? diskmax : RAID_PARITY_MAX;
+	waiting_map = malloc_nofail(waiting_mac * sizeof(unsigned));
 
 	error = 0;
 	io_error = 0;
diff --git a/cmdline/scrub.c b/cmdline/scrub.c
index c828a7e4..bd582199 100644
--- a/cmdline/scrub.c
+++ b/cmdline/scrub.c
@@ -279,7 +279,9 @@ static int state_scrub_process(struct snapraid_state* state, struct snapraid_par
 	/* initialize the io threads */
 	io_init(&io, state, state->opt.io_cache, buffermax, scrub_data_reader, handle, diskmax, scrub_parity_reader, 0, parity_handle, state->level);
 
-	waiting_map = malloc_nofail((diskmax + RAID_PARITY_MAX) * sizeof(unsigned));
+	/* possibly waiting disks */
+	waiting_mac = diskmax > RAID_PARITY_MAX ? diskmax : RAID_PARITY_MAX;
+	waiting_map = malloc_nofail(waiting_mac * sizeof(unsigned));
 
 	error = 0;
 	silent_error = 0;
diff --git a/cmdline/sync.c b/cmdline/sync.c
index b597b03a..c33a5a3e 100644
--- a/cmdline/sync.c
+++ b/cmdline/sync.c
@@ -713,7 +713,10 @@ static int state_sync_process(struct snapraid_state* state, struct snapraid_pari
 
 	failed = malloc_nofail(diskmax * sizeof(struct failed_struct));
 	failed_map = malloc_nofail(diskmax * sizeof(unsigned));
-	waiting_map = malloc_nofail((diskmax + RAID_PARITY_MAX) * sizeof(unsigned));
+
+	/* possibly waiting disks */
+	waiting_mac = diskmax > RAID_PARITY_MAX ? diskmax : RAID_PARITY_MAX;
+	waiting_map = malloc_nofail(waiting_mac * sizeof(unsigned));
 
 	error = 0;
 	silent_error = 0;