diff --git a/index.js b/index.js
index 0da3a56..6f78774 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,6 @@
 module.exports = function (blocking) {
   [process.stdout, process.stderr].forEach(function (stream) {
-    if (stream._handle && typeof stream._handle.setBlocking === 'function') {
+    if (stream._handle && stream.isTTY && typeof stream._handle.setBlocking === 'function') {
       stream._handle.setBlocking(blocking)
     }
   })
diff --git a/test/fixtures/yargs-497-stderr.js b/test/fixtures/yargs-497-stderr.js
index 9b498af..1362d61 100755
--- a/test/fixtures/yargs-497-stderr.js
+++ b/test/fixtures/yargs-497-stderr.js
@@ -1,5 +1,9 @@
 #!/usr/bin/env node
 
+// pretend we are a TTY
+process.stdout.isTTY = true
+process.stderr.isTTY = true
+
 // see: https://github.com/yargs/yargs/issues/497
 var buffer = ''
 for (var i = 0; i < 3000; i++) {
diff --git a/test/fixtures/yargs-497-stdout.js b/test/fixtures/yargs-497-stdout.js
index fdc792a..ae29976 100755
--- a/test/fixtures/yargs-497-stdout.js
+++ b/test/fixtures/yargs-497-stdout.js
@@ -1,5 +1,9 @@
 #!/usr/bin/env node
 
+// pretend we are a TTY
+process.stdout.isTTY = true
+process.stderr.isTTY = true
+
 // see: https://github.com/yargs/yargs/issues/497
 var buffer = ''
 for (var i = 0; i < 3000; i++) {