diff --git a/tests/fuzz/fuzz.py b/tests/fuzz/fuzz.py
index c790c8373..9df68df0c 100755
--- a/tests/fuzz/fuzz.py
+++ b/tests/fuzz/fuzz.py
@@ -660,7 +660,7 @@ def gen_parser(args):
     parser.add_argument(
         '--max-size-log',
         type=int,
-        default=13,
+        default=18,
         help='Maximum sample size to generate')
     parser.add_argument(
         '--seed',
@@ -720,7 +720,7 @@ def gen(args):
             if info.frame_type == FrameType.BLOCK:
                 cmd += [
                     '--gen-blocks',
-                    '--max-block-size-log={}'.format(args.max_size_log)
+                    '--max-block-size-log={}'.format(min(args.max_size_log, 17))
                 ]
             else:
                 cmd += ['--max-content-size-log={}'.format(args.max_size_log)]