diff --git a/lib/cli/Shell.php b/lib/cli/Shell.php
index 037fe77..b9ae380 100755
--- a/lib/cli/Shell.php
+++ b/lib/cli/Shell.php
@@ -112,8 +112,12 @@ static public function hide($hidden = true) {
 	 *
 	 * @return bool
 	 */
-	static private function is_windows() {
-		return strtoupper(substr(PHP_OS, 0, 3)) === 'WIN';
+	static public function is_windows() {
+		$test_is_windows = getenv( 'WP_CLI_TEST_IS_WINDOWS' );
+		if ( false !== $test_is_windows ) {
+			return (bool) $test_is_windows;
+		}
+		return strtoupper( substr( PHP_OS, 0, 3 ) ) === 'WIN';
 	}
 
 }
diff --git a/lib/cli/progress/Bar.php b/lib/cli/progress/Bar.php
index 43f21b5..9c58f76 100644
--- a/lib/cli/progress/Bar.php
+++ b/lib/cli/progress/Bar.php
@@ -82,6 +82,10 @@ public function display($finish = false) {
 		$timing    = Streams::render($this->_formatTiming, compact('elapsed', 'estimated', 'current', 'total', 'percent'));
 
 		$size = Shell::columns();
+		// On Windows, the cursor wraps to the next line if the output fills the entire width.
+		if ( Shell::is_windows() ) {
+			$size -= 1;
+		}
 		$size -= strlen($msg . $timing);
 		if ( $size < 0 ) {
 			$size = 0;