diff --git a/dangerzone/__init__.py b/dangerzone/__init__.py
index bcf4013..28a8671 100644
--- a/dangerzone/__init__.py
+++ b/dangerzone/__init__.py
@@ -1,4 +1,5 @@
 from PyQt5 import QtCore, QtWidgets
+import os
 import sys
 import signal
 import click
@@ -39,6 +40,17 @@ def main(filename):
             return
 
         filename = filename[0]
+    else:
+        # Validate filename
+        filename = os.path.abspath(os.path.expanduser(filename))
+        try:
+            open(filename, "rb")
+        except FileNotFoundError:
+            print("File not found")
+            return
+        except PermissionError:
+            print("Permission denied")
+            return
 
     main_window.start(filename)
     sys.exit(app.exec_())
diff --git a/dangerzone/main_window.py b/dangerzone/main_window.py
index 258e403..3760929 100644
--- a/dangerzone/main_window.py
+++ b/dangerzone/main_window.py
@@ -10,8 +10,8 @@ class MainWindow(QtWidgets.QMainWindow):
         self.common = common
 
         self.setWindowTitle("dangerzone")
-        self.setMinimumWidth(600)
-        self.setMinimumHeight(500)
+        self.setMinimumWidth(500)
+        self.setMinimumHeight(400)
 
         self.task_label = QtWidgets.QLabel()
         self.task_label.setAlignment(QtCore.Qt.AlignCenter)
diff --git a/dangerzone/tasks.py b/dangerzone/tasks.py
index 57a79e7..40247ed 100644
--- a/dangerzone/tasks.py
+++ b/dangerzone/tasks.py
@@ -54,9 +54,9 @@ class BuildContainerTask(TaskBase):
         self.common = common
 
     def run(self):
-        containerfile = self.common.get_resource_path("Containerfile")
+        container_path = self.common.get_resource_path("container")
         self.update_label.emit("Building container")
         self.update_details.emit("")
-        args = ["podman", "build", "-t", "dangerzone", "-f", containerfile]
+        args = ["podman", "build", "-t", "dangerzone", container_path]
         self.execute_podman(args)
         self.thread_finished.emit()
diff --git a/share/Containerfile b/share/container/Containerfile
similarity index 100%
rename from share/Containerfile
rename to share/container/Containerfile