diff --git a/lib/client.js b/lib/client.js
index 968a7f92071..056cc97a35f 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -1183,7 +1183,7 @@ async function connect (client) {
     const idx = hostname.indexOf(']')
 
     assert(idx !== -1)
-    const ip = hostname.substr(1, idx - 1)
+    const ip = hostname.substring(1, idx)
 
     assert(net.isIP(ip))
     hostname = ip
diff --git a/lib/core/util.js b/lib/core/util.js
index 7fe2229c3c4..52c6b985883 100644
--- a/lib/core/util.js
+++ b/lib/core/util.js
@@ -125,13 +125,13 @@ function getHostname (host) {
     const idx = host.indexOf(']')
 
     assert(idx !== -1)
-    return host.substr(1, idx - 1)
+    return host.substring(1, idx)
   }
 
   const idx = host.indexOf(':')
   if (idx === -1) return host
 
-  return host.substr(0, idx)
+  return host.substring(0, idx)
 }
 
 // IP addresses are not valid server names per RFC6066