diff --git a/src/Console/Terminal.php b/src/Console/Terminal.php
index 8b585bf3..1e438135 100644
--- a/src/Console/Terminal.php
+++ b/src/Console/Terminal.php
@@ -54,7 +54,7 @@ private static function initDimensions(): void
     {
         $consoleMode = self::getConsoleMode();
 
-        if ('\\' === \DIRECTORY_SEPARATOR) {
+        if ('\\' === \DIRECTORY_SEPARATOR && is_string(\getenv('ANSICON'))) {
             if (\preg_match('#^(\d+)x(\d+)(?: \((\d+)x(\d+)\))?$#', \trim(\getenv('ANSICON')), $matches)) {
                 self::$width = (int) $matches[1];
             } elseif (! self::hasVt100Support() && self::hasSttyAvailable()) {