diff --git a/src/ui/RenderDebouncer.ts b/src/ui/RenderDebouncer.ts
index 260de12e..ee2ab16e 100644
--- a/src/ui/RenderDebouncer.ts
+++ b/src/ui/RenderDebouncer.ts
@@ -3,40 +3,37 @@
  * @license MIT
  */
 
-import { IDisposable } from 'xterm';
+import { IDisposable } from '../common/Types';
 
 /**
  * Debounces calls to render terminal rows using animation frames.
  */
 export class RenderDebouncer implements IDisposable {
-  private _rowStart: number;
-  private _rowEnd: number;
-  private _rowCount: number;
-  private _animationFrame: number = null;
+  private _rowStart: number | undefined;
+  private _rowEnd: number | undefined;
+  private _rowCount: number | undefined;
+  private _animationFrame: number | undefined;
 
   constructor(
-    private _callback: (start: number, end: number) => void
+    private _renderCallback: (start: number, end: number) => void
   ) {
   }
 
   public dispose(): void {
     if (this._animationFrame) {
       window.cancelAnimationFrame(this._animationFrame);
-      this._animationFrame = null;
+      this._animationFrame = undefined;
     }
   }
 
   public refresh(rowStart: number, rowEnd: number, rowCount: number): void {
     this._rowCount = rowCount;
     // Get the min/max row start/end for the arg values
-    rowStart = rowStart !== null && rowStart !== undefined ? rowStart : 0;
-    rowEnd = rowEnd !== null && rowEnd !== undefined ? rowEnd : this._rowCount - 1;
-    // Check whether the row start/end values have already been set
-    const isRowStartSet = this._rowStart !== undefined && this._rowStart !== null;
-    const isRowEndSet = this._rowEnd !== undefined && this._rowEnd !== null;
+    rowStart = rowStart !== undefined ? rowStart : 0;
+    rowEnd = rowEnd !== undefined ? rowEnd : this._rowCount - 1;
     // Set the properties to the updated values
-    this._rowStart = isRowStartSet ? Math.min(this._rowStart, rowStart) : rowStart;
-    this._rowEnd = isRowEndSet ? Math.max(this._rowEnd, rowEnd) : rowEnd;
+    this._rowStart = this._rowStart !== undefined ? Math.min(this._rowStart, rowStart) : rowStart;
+    this._rowEnd = this._rowEnd !== undefined ? Math.max(this._rowEnd, rowEnd) : rowEnd;
 
     if (this._animationFrame) {
       return;
@@ -46,16 +43,21 @@ export class RenderDebouncer implements IDisposable {
   }
 
   private _innerRefresh(): void {
+    // Make sure values are set
+    if (this._rowStart === undefined || this._rowEnd === undefined || this._rowCount === undefined) {
+      return;
+    }
+
     // Clamp values
     this._rowStart = Math.max(this._rowStart, 0);
     this._rowEnd = Math.min(this._rowEnd, this._rowCount - 1);
 
     // Run render callback
-    this._callback(this._rowStart, this._rowEnd);
+    this._renderCallback(this._rowStart, this._rowEnd);
 
     // Reset debouncer
-    this._rowStart = null;
-    this._rowEnd = null;
-    this._animationFrame = null;
+    this._rowStart = undefined;
+    this._rowEnd = undefined;
+    this._animationFrame = undefined;
   }
 }
diff --git a/src/ui/tsconfig.json b/src/ui/tsconfig.json
index 2763c6b1..672d464e 100644
--- a/src/ui/tsconfig.json
+++ b/src/ui/tsconfig.json
@@ -11,7 +11,8 @@
     ]
   },
   "include": [
-    "./Lifecycle.ts"
+    "./Lifecycle.ts",
+    "./RenderDebouncer.ts"
   ],
   "references": [
     { "path": "../common" }