diff --git a/Headers/AppKit/NSWindow.h b/Headers/AppKit/NSWindow.h
index 54481cba6..90d1c70bb 100644
--- a/Headers/AppKit/NSWindow.h
+++ b/Headers/AppKit/NSWindow.h
@@ -570,8 +570,8 @@ PACKAGE_SCOPE
 - (NSResponder*) firstResponder;
 
 #if OS_API_VERSION(MAC_OS_X_VERSION_10_5, GS_API_LATEST)
-- (NSWindowCollectionBehavior)collectionBehaviour;
-- (void)setCollectionBehaviour:(NSWindowCollectionBehavior)props;
+- (NSWindowCollectionBehavior)collectionBehavior;
+- (void)setCollectionBehavior:(NSWindowCollectionBehavior)props;
 #endif
 
 /**
diff --git a/Source/NSWindow.m b/Source/NSWindow.m
index 56a471928..638382c74 100644
--- a/Source/NSWindow.m
+++ b/Source/NSWindow.m
@@ -2657,13 +2657,13 @@ titleWithRepresentedFilename(NSString *representedFilename)
   _f.dynamic_depth_limit = flag;
 }
 
-- (NSWindowCollectionBehavior)collectionBehaviour
+- (NSWindowCollectionBehavior)collectionBehavior
 {
   //TODO: we don't handle collections yet and perhaps never will fully
   return 0;
 }
 
-- (void)setCollectionBehaviour:(NSWindowCollectionBehavior)props
+- (void)setCollectionBehavior:(NSWindowCollectionBehavior)props
 {
   //TODO we don't handle collections yet. Perhaps certain features can be mapped on existing ones
   //other features are Expose specific or anyway probably not implementable