diff --git a/Source/NSHelpManager.m b/Source/NSHelpManager.m
index 56e8afb1e..75b41baf9 100644
--- a/Source/NSHelpManager.m
+++ b/Source/NSHelpManager.m
@@ -30,6 +30,7 @@
 #include <Foundation/NSFileManager.h>
 #include <Foundation/NSString.h>
 #include <Foundation/NSBundle.h>
+#include <Foundation/NSArchiver.h>
 #include <AppKit/NSAttributedString.h>
 #include <AppKit/NSApplication.h>
 #include <AppKit/NSWorkspace.h>