diff --git a/lib/internal/blocklist.js b/lib/internal/blocklist.js
index 0ad58373b746b2..28a31caa165e09 100644
--- a/lib/internal/blocklist.js
+++ b/lib/internal/blocklist.js
@@ -55,6 +55,7 @@ class BlockList {
       throw new ERR_INVALID_ARG_TYPE('address', 'string', address);
     if (typeof family !== 'string')
       throw new ERR_INVALID_ARG_TYPE('family', 'string', family);
+    family = family.toLowerCase();
     if (family !== 'ipv4' && family !== 'ipv6')
       throw new ERR_INVALID_ARG_VALUE('family', family);
     const type = family === 'ipv4' ? AF_INET : AF_INET6;
@@ -68,6 +69,7 @@ class BlockList {
       throw new ERR_INVALID_ARG_TYPE('end', 'string', end);
     if (typeof family !== 'string')
       throw new ERR_INVALID_ARG_TYPE('family', 'string', family);
+    family = family.toLowerCase();
     if (family !== 'ipv4' && family !== 'ipv6')
       throw new ERR_INVALID_ARG_VALUE('family', family);
     const type = family === 'ipv4' ? AF_INET : AF_INET6;
@@ -83,6 +85,7 @@ class BlockList {
       throw new ERR_INVALID_ARG_TYPE('prefix', 'number', prefix);
     if (typeof family !== 'string')
       throw new ERR_INVALID_ARG_TYPE('family', 'string', family);
+    family = family.toLowerCase();
     let type;
     switch (family) {
       case 'ipv4':
@@ -106,6 +109,7 @@ class BlockList {
       throw new ERR_INVALID_ARG_TYPE('address', 'string', address);
     if (typeof family !== 'string')
       throw new ERR_INVALID_ARG_TYPE('family', 'string', family);
+    family = family.toLowerCase();
     if (family !== 'ipv4' && family !== 'ipv6')
       throw new ERR_INVALID_ARG_VALUE('family', family);
     const type = family === 'ipv4' ? AF_INET : AF_INET6;
diff --git a/test/parallel/test-blocklist.js b/test/parallel/test-blocklist.js
index cef90dc9a10e08..24f85e0f1b40f4 100644
--- a/test/parallel/test-blocklist.js
+++ b/test/parallel/test-blocklist.js
@@ -56,6 +56,7 @@ const assert = require('assert');
   assert(blockList.check('8592:757c:efae:4e45:fb5d:d62a:0d00:8e17', 'ipv6'));
 
   assert(blockList.check('::ffff:1.1.1.1', 'ipv6'));
+  assert(blockList.check('::ffff:1.1.1.1', 'IPV6'));
 
   assert(blockList.check('1.1.1.2'));
 
@@ -100,7 +101,7 @@ const assert = require('assert');
   const blockList = new BlockList();
   blockList.addAddress('1.1.1.1');
   blockList.addRange('10.0.0.1', '10.0.0.10');
-  blockList.addSubnet('8592:757c:efae:4e45::', 64, 'ipv6');
+  blockList.addSubnet('8592:757c:efae:4e45::', 64, 'IpV6'); // Case insensitive
 
   const rulesCheck = [
     'Subnet: IPv6 8592:757c:efae:4e45::/64',