diff --git a/scripts/pubkey_speed.c b/scripts/pubkey_speed.c
index 83ab4e41b..21e4d2c1e 100644
--- a/scripts/pubkey_speed.c
+++ b/scripts/pubkey_speed.c
@@ -56,6 +56,10 @@ int main(int argc, char *argv[])
 	}
 
 	rounds = atoi(argv[3]);
+	if (rounds < 0 || rounds > (2^26))
+	{	/* arbitrary limit to the number of chunk_t/sigs that fit into 1 GiB */
+		usage();
+	}
 
 	if (streq(argv[2], "rsa"))
 	{