diff --git a/lib/tls.js b/lib/tls.js
index 849daeb07f3456..765e1658ea9127 100644
--- a/lib/tls.js
+++ b/lib/tls.js
@@ -49,22 +49,19 @@ function convertProtocols(protocols) {
 exports.convertNPNProtocols = function(protocols, out) {
   // If protocols is Array - translate it into buffer
   if (Array.isArray(protocols)) {
-    protocols = convertProtocols(protocols);
-  }
-  // If it's already a Buffer - store it
-  if (protocols instanceof Buffer) {
-    out.NPNProtocols = protocols;
+    out.NPNProtocols = convertProtocols(protocols);
+  } else if (protocols instanceof Buffer) {
+    // Copy new buffer not to be modified by user.
+    out.NPNProtocols = Buffer.from(protocols);
   }
 };
 
 exports.convertALPNProtocols = function(protocols, out) {
   // If protocols is Array - translate it into buffer
   if (Array.isArray(protocols)) {
-    protocols = convertProtocols(protocols);
-  }
-  // If it's already a Buffer - store it
-  if (protocols instanceof Buffer) {
-    // copy new buffer not to be modified by user
+    out.ALPNProtocols = convertProtocols(protocols);
+  } else if (protocols instanceof Buffer) {
+    // Copy new buffer not to be modified by user.
     out.ALPNProtocols = Buffer.from(protocols);
   }
 };
diff --git a/test/parallel/test-tls-basic-validations.js b/test/parallel/test-tls-basic-validations.js
index a741f3b49c47ac..edf47f7059b406 100644
--- a/test/parallel/test-tls-basic-validations.js
+++ b/test/parallel/test-tls-basic-validations.js
@@ -33,3 +33,21 @@ assert.throws(() => tls.createServer({ticketKeys: new Buffer(0)}),
 
 assert.throws(() => tls.createSecurePair({}),
               /Error: First argument must be a tls module SecureContext/);
+
+{
+  const buffer = Buffer.from('abcd');
+  const out = {};
+  tls.convertALPNProtocols(buffer, out);
+  out.ALPNProtocols.write('efgh');
+  assert(buffer.equals(Buffer.from('abcd')));
+  assert(out.ALPNProtocols.equals(Buffer.from('efgh')));
+}
+
+{
+  const buffer = Buffer.from('abcd');
+  const out = {};
+  tls.convertNPNProtocols(buffer, out);
+  out.NPNProtocols.write('efgh');
+  assert(buffer.equals(Buffer.from('abcd')));
+  assert(out.NPNProtocols.equals(Buffer.from('efgh')));
+}