diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5b34e904..c27c80f0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,6 +8,7 @@ on:
   pull_request:
     branches:
       - master
+      - v5.x
     paths-ignore:
       - '**.md'
 jobs:
diff --git a/lib/types.js b/lib/types.js
index f4d644e6..dc7c69cf 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -15,11 +15,10 @@
  */
 
 var utils = require('./utils'),
-    buffer = require('buffer'), // For `SlowBuffer`.
+    buffer = require('buffer'),
     util = require('util');
 
 var Buffer = buffer.Buffer;
-var SlowBuffer = buffer.SlowBuffer;
 
 // Convenience imports.
 var Tap = utils.Tap;
@@ -48,7 +47,7 @@ var TYPES = {
 var RANDOM = new utils.Lcg();
 
 // Encoding tap (shared for performance).
-var TAP = new Tap(new SlowBuffer(1024));
+var TAP = new Tap(utils.newSlowBuffer(1024));
 
 // Currently active logical type, used for name redirection.
 var LOGICAL_TYPE = null;
@@ -453,7 +452,7 @@ Type.isType = function (/* any, [prefix] ... */) {
 
 Type.__reset = function (size) {
   debug('resetting type buffer to %d', size);
-  TAP.buf = new SlowBuffer(size);
+  TAP.buf = utils.newSlowBuffer(size);
 };
 
 Object.defineProperty(Type.prototype, 'branchName', {
diff --git a/lib/utils.js b/lib/utils.js
index d8c525bd..cd0cb41a 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -11,7 +11,7 @@ var buffer = require('buffer');
 var crypto = require('crypto');
 var util = require('util');
 
-var Buffer = buffer.Buffer; 
+var Buffer = buffer.Buffer;
 
 // Shared buffer pool for all taps.
 var POOL = new BufferPool(4096);
@@ -35,6 +35,14 @@ function newBuffer(size) {
   }
 }
 
+function newSlowBuffer(size) {
+  if (typeof Buffer.allocUnsafeSlow == 'function') {
+    return Buffer.allocUnsafeSlow(size);
+  } else {
+    return new buffer.SlowBuffer(size);
+  }
+}
+
 /**
  * Create a new buffer with the input contents.
  *
@@ -952,6 +960,7 @@ module.exports = {
   isValidName: isValidName,
   jsonEnd: jsonEnd,
   newBuffer: newBuffer,
+  newSlowBuffer: newSlowBuffer,
   objectValues: objectValues,
   qualify: qualify,
   toMap: toMap,