diff --git a/Source/DocMakefile b/Source/DocMakefile
index d415e5121..6bb15fa62 100644
--- a/Source/DocMakefile
+++ b/Source/DocMakefile
@@ -64,6 +64,7 @@ NSFormatter.h \
 NSGeometry.h \
 NSHashTable.h \
 NSHost.h \
+NSIndexSet.h \
 NSInvocation.h \
 NSKeyedArchiver.h \
 NSKeyValueCoding.h \