diff --git a/arb_poly/mullow.c b/arb_poly/mullow.c
index dd41c3b2..99f5d53b 100644
--- a/arb_poly/mullow.c
+++ b/arb_poly/mullow.c
@@ -25,7 +25,7 @@
 
 #include "arb_poly.h"
 
-#define BLOCK_CUTOFF 18
+#define BLOCK_CUTOFF 16
 
 void
 _arb_poly_mullow(arb_ptr res,