diff --git a/lib/vtt.js b/lib/vtt.js
index 66ab23f..d664c99 100644
--- a/lib/vtt.js
+++ b/lib/vtt.js
@@ -925,7 +925,11 @@
       // video, depending on the writing direction, and reverse our axis directions.
       if (linePos < 0) {
         position += cue.vertical === "" ? containerBox.height : containerBox.width;
-        axis = axis.reverse();
+
+        // Safari 12 introduced a bug where the reverse order of an array is cached after calling
+        // array.prototype.reverse (https://bugs.webkit.org/show_bug.cgi?id=188794).
+        // As a workaround, call reverse on a copy of the 'axis' array, instead of calling it directly on the original var
+        axis = axis.slice().reverse();
       }
 
       // Move the box to the specified position. This may not be its best