diff --git a/butterfly/static/coffees/term.coffee b/butterfly/static/coffees/term.coffee
index 467cfea..f48db57 100644
--- a/butterfly/static/coffees/term.coffee
+++ b/butterfly/static/coffees/term.coffee
@@ -1408,10 +1408,10 @@ class Terminal
         if j < @rows
             el = @element
             while j++ < @rows
-                @lines.push @blankLine() if @lines.length < y + @ybase
+                @lines.push @blankLine() if @lines.length < @rows + @ybase
                 if @children.length < @rows
                     line = @document.createElement("div")
-                    @line.className = 'line'
+                    line.className = 'line'
                     line.style.height = @char_size.height + 'px'
                     el.appendChild line
                     @children.push line
diff --git a/butterfly/static/javascripts/main.js b/butterfly/static/javascripts/main.js
index 7511f26..f4532a7 100644
--- a/butterfly/static/javascripts/main.js
+++ b/butterfly/static/javascripts/main.js
@@ -1334,12 +1334,12 @@ Terminal = (function() {
     if (j < this.rows) {
       el = this.element;
       while (j++ < this.rows) {
-        if (this.lines.length < y + this.ybase) {
+        if (this.lines.length < this.rows + this.ybase) {
           this.lines.push(this.blankLine());
         }
         if (this.children.length < this.rows) {
           line = this.document.createElement("div");
-          this.line.className = 'line';
+          line.className = 'line';
           line.style.height = this.char_size.height + 'px';
           el.appendChild(line);
           this.children.push(line);