diff --git a/src/prime.h b/src/prime.h
index d470c2cd..5e830883 100644
--- a/src/prime.h
+++ b/src/prime.h
@@ -21,7 +21,7 @@
 
 // Used for resizing hash tables.
 // Values approximately double.
-// http://planetmath.org/encyclopedia/GoodHashTablePrimes.html
+// https://planetmath.org/goodhashtableprimes
 static int primes[] = {
 	5,
 	13,