diff --git a/baseconv.c b/baseconv.c
index 33ecad4..5ec5e3d 100644
--- a/baseconv.c
+++ b/baseconv.c
@@ -9,7 +9,7 @@ static const char digits[] = "0123456789abcdefghijklmnopqrstuvwxyz";
 bool baseconv(char outbuf[], size_t bufsize, unsigned base, uintmax_t num) {
 	// Supported bases are 2 to 36 inclusive (though it could be higher
 	// if our digits string was longer
-	if (base < 2 || base > 36)
+	if (base < 2 || base > sizeof(digits))
 		return false;
 
 	// Longest possible converted string is base-2, where we produce one