diff --git a/SilicaViewer/Document.swift b/SilicaViewer/Document.swift
index 95a12b8..797a241 100644
--- a/SilicaViewer/Document.swift
+++ b/SilicaViewer/Document.swift
@@ -133,17 +133,14 @@ class Document: NSDocument {
     }
     
     /*
-     Parses the chunk filename, ex. 1~1 to integer coordinates.
+     Parses the chunk filename, ex. "1~1.chunk" to integer coordinates (1, 2).
      */
     func parseChunkFilename(_ filename: String) -> (Int, Int)? {
         let pathURL = URL(fileURLWithPath: filename)
         let pathComponents = pathURL.lastPathComponent.replacingOccurrences(of: ".chunk", with: "").components(separatedBy: "~")
         
-        let x = Int(pathComponents[0])
-        let y = Int(pathComponents[1])
-        
-        if x != nil && y != nil {
-            return (x!, y! + 1)
+        if let x = Int(pathComponents[0]), let y = Int(pathComponents[1]) {
+            return (x, y + 1)
         } else {
             return nil
         }