diff --git a/Mac/OSX/PythonLauncher/MyAppDelegate.h b/Mac/OSX/PythonLauncher/MyAppDelegate.h
index c65175a..097b541 100644
--- a/Mac/OSX/PythonLauncher/MyAppDelegate.h
+++ b/Mac/OSX/PythonLauncher/MyAppDelegate.h
@@ -11,4 +11,5 @@
 - (IBAction)showPreferences:(id)sender;
 - (BOOL)shouldShowUI;
 - (BOOL)shouldTerminate;
+- (void)testFileTypeBinding;
 @end
diff --git a/Mac/OSX/PythonLauncher/MyAppDelegate.m b/Mac/OSX/PythonLauncher/MyAppDelegate.m
index cb97972..a5ba751 100644
--- a/Mac/OSX/PythonLauncher/MyAppDelegate.m
+++ b/Mac/OSX/PythonLauncher/MyAppDelegate.m
@@ -1,6 +1,7 @@
 #import "MyAppDelegate.h"
 #import "PreferencesWindowController.h"
 #import <Carbon/Carbon.h>
+#import <ApplicationServices/ApplicationServices.h>
 
 @implementation MyAppDelegate
 
@@ -19,6 +20,8 @@
 
 - (void)applicationDidFinishLaunching:(NSNotification *)notification
 {
+    // Test that the file mappings are correct
+    [self testFileTypeBinding];
     // If we were opened because of a file drag or doubleclick
     // we've set initial_action_done in shouldShowUI
     // Otherwise we open a preferences dialog.
@@ -50,4 +53,44 @@
     return NO;
 }
 
+- (void)testFileTypeBinding
+{
+    NSURL *ourUrl;
+    OSStatus err;
+    FSRef appRef;
+    NSURL *appUrl;
+    static NSString *extensions[] = { @"py", @"pyw", @"pyc", NULL};
+    NSString **ext_p;
+    int i;
+    
+    if ([[NSUserDefaults standardUserDefaults] boolForKey: @"SkipFileBindingTest"])
+        return;
+    ourUrl = [NSURL fileURLWithPath: [[NSBundle mainBundle] bundlePath]];
+    for( ext_p = extensions; *ext_p; ext_p++ ) {
+        err = LSGetApplicationForInfo(
+            kLSUnknownType,
+            kLSUnknownCreator,
+            (CFStringRef)*ext_p,
+            kLSRolesViewer,
+            &appRef,
+            (CFURLRef *)&appUrl);
+        if (err || ![appUrl isEqual: ourUrl] ) {
+            i = NSRunAlertPanel(@"File type binding",
+                @"PythonLauncher is not the default application for all " \
+                  @"Python script types. You should fix this with the " \
+                  @"Finder's \"Get Info\" command.\n\n" \
+                  @"See \"Changing the application that opens a file\" in " \
+                  @"Mac Help for details.",
+                @"OK",
+                @"Don't show this warning again",
+                NULL);
+            if ( i == 0 ) { // Don't show again
+                [[NSUserDefaults standardUserDefaults]
+                    setObject:@"YES" forKey:@"SkipFileBindingTest"];
+            }
+            return;
+        }
+    }
+}
+        
 @end
diff --git a/Mac/OSX/PythonLauncher/PythonLauncher.pbproj/project.pbxproj b/Mac/OSX/PythonLauncher/PythonLauncher.pbproj/project.pbxproj
index 5b4a06c..107ce3d 100755
--- a/Mac/OSX/PythonLauncher/PythonLauncher.pbproj/project.pbxproj
+++ b/Mac/OSX/PythonLauncher/PythonLauncher.pbproj/project.pbxproj
@@ -320,24 +320,6 @@
 		<dict>
 			<key>CFBundleTypeExtensions</key>
 			<array>
-				<string>????</string>
-			</array>
-			<key>CFBundleTypeIconFile</key>
-			<string></string>
-			<key>CFBundleTypeName</key>
-			<string>DocumentType</string>
-			<key>CFBundleTypeOSTypes</key>
-			<array>
-				<string>????</string>
-			</array>
-			<key>CFBundleTypeRole</key>
-			<string>Editor</string>
-			<key>NSDocumentClass</key>
-			<string>MyDocument</string>
-		</dict>
-		<dict>
-			<key>CFBundleTypeExtensions</key>
-			<array>
 				<string>py</string>
 			</array>
 			<key>CFBundleTypeIconFile</key>