diff --git a/lib/ace/document.js b/lib/ace/document.js
index e60dbbd7..c58b70bb 100644
--- a/lib/ace/document.js
+++ b/lib/ace/document.js
@@ -293,7 +293,7 @@ var Document = function(text, mode) {
 
     this.getScreenWidth = function() {
         this.$computeWidth();
-        return this.screenWith;
+        return this.screenWidth;
     };
 
     this.$computeWidth = function() {
@@ -316,7 +316,7 @@ var Document = function(text, mode) {
                 longestScreenLine = Math.max(longestScreenLine, len);
             }
             this.width = longestLine;
-            this.screenWith = longestScreenLine;
+            this.screenWidth = longestScreenLine;
         }
     };