diff --git a/DBPrefsWindowController.h b/DBPrefsWindowController.h
index 63b7855..63a80d0 100644
--- a/DBPrefsWindowController.h
+++ b/DBPrefsWindowController.h
@@ -42,7 +42,7 @@
 #import <Cocoa/Cocoa.h>
 
 
-@interface DBPrefsWindowController : NSWindowController /*<NSAnimationDelegate,NSToolbarDelegate>*/{
+@interface DBPrefsWindowController : NSWindowController PROTOCOL_10_6(NSAnimationDelegate,NSToolbarDelegate){
 	NSMutableArray *toolbarIdentifiers;
 	NSMutableDictionary *toolbarViews;
 	NSMutableDictionary *toolbarItems;
diff --git a/GitX_Prefix.pch b/GitX_Prefix.pch
index f1ce03e..0af9ac2 100644
--- a/GitX_Prefix.pch
+++ b/GitX_Prefix.pch
@@ -17,3 +17,16 @@
 #ifndef ALog
 #define ALog(...) DLog(__VA_ARGS__)
 #endif
+
+// In 10.6, some NSObject categories (like NSWindowDelegate) were changed to
+// protocols. Thus to avoid warnings we need to add protocol specifiers, but
+// only when compiling for 10.6+.
+#ifndef MAC_OS_X_VERSION_10_6
+#define MAC_OS_X_VERSION_10_6 1060
+#endif
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6
+#define PROTOCOL_10_6(...) <__VA_ARGS__>
+#else
+#define PROTOCOL_10_6(...)
+#endif
diff --git a/PBGitHistoryController.h b/PBGitHistoryController.h
index f9cf468..a09bc64 100644
--- a/PBGitHistoryController.h
+++ b/PBGitHistoryController.h
@@ -22,7 +22,7 @@
 
 @class PBHistorySearchController;
 
-@interface PBGitHistoryController : PBViewController /*<NSOutlineViewDelegate>*/{
+@interface PBGitHistoryController : PBViewController PROTOCOL_10_6(NSOutlineViewDelegate){
 	IBOutlet PBRefController *refController;
 	IBOutlet NSSearchField *searchField;
 	IBOutlet NSArrayController* commitController;
diff --git a/PBGitSidebarController.h b/PBGitSidebarController.h
index 623c816..64fd606 100644
--- a/PBGitSidebarController.h
+++ b/PBGitSidebarController.h
@@ -13,7 +13,7 @@
 @class PBGitHistoryController;
 @class PBGitCommitController;
 
-@interface PBGitSidebarController : PBViewController /*<NSOutlineViewDelegate>*/{
+@interface PBGitSidebarController : PBViewController PROTOCOL_10_6(NSOutlineViewDelegate, NSMenuDelegate){
 	IBOutlet NSWindow *window;
 	IBOutlet NSOutlineView *sourceView;
 	IBOutlet NSView *sourceListControlsView;
diff --git a/PBGitWindowController.h b/PBGitWindowController.h
index c844bf6..a3bb3cb 100644
--- a/PBGitWindowController.h
+++ b/PBGitWindowController.h
@@ -14,7 +14,7 @@
 
 @class PBViewController, PBGitSidebarController, PBGitCommitController;
 
-@interface PBGitWindowController : NSWindowController /*<NSWindowDelegate>*/{
+@interface PBGitWindowController : NSWindowController PROTOCOL_10_6(NSWindowDelegate){
 	__weak PBGitRepository* repository;
 
 	PBViewController *contentController;