diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index b06e8b0a1..ec05ce27c 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -1761,7 +1761,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
             fontFamily: font.fallbackName,
             ascent: font.ascent,
             descent: font.descent,
-            vertical: !!font.vertical,
+            vertical: font.vertical,
           };
         }
         textContentItem.fontName = font.loadedName;
diff --git a/src/core/fonts.js b/src/core/fonts.js
index 00a721aa9..81136c650 100644
--- a/src/core/fonts.js
+++ b/src/core/fonts.js
@@ -607,7 +607,7 @@ var Font = (function FontClosure() {
     }
 
     this.cidEncoding = properties.cidEncoding;
-    this.vertical = properties.vertical;
+    this.vertical = !!properties.vertical;
     if (this.vertical) {
       this.vmetrics = properties.vmetrics;
       this.defaultVMetrics = properties.defaultVMetrics;