diff --git a/tests/lua53/strings.lua b/tests/lua53/strings.lua
index db950dd..0522bf9 100644
--- a/tests/lua53/strings.lua
+++ b/tests/lua53/strings.lua
@@ -55,13 +55,13 @@ a,b = string.find("123456789", "345")
 assert(string.sub("123456789", a, b) == "345")
 assert(string.find("1234567890123456789", "345", 3) == 3)
 assert(string.find("1234567890123456789", "345", 4) == 13)
-assert(string.find("1234567890123456789", "346", 4) == nil)
+assert(not string.find("1234567890123456789", "346", 4))
 assert(string.find("1234567890123456789", ".45", -9) == 13)
-assert(string.find("abcdefg", "\0", 5, 1) == nil)
+assert(not string.find("abcdefg", "\0", 5, 1))
 assert(string.find("", "") == 1)
 assert(string.find("", "", 1) == 1)
 assert(not string.find("", "", 2))
-assert(string.find('', 'aaa', 1) == nil)
+assert(not string.find('', 'aaa', 1))
 assert(('alo(.)alo'):find('(.)', 1, 1) == 4)
 
 assert(string.len("") == 0)