diff --git a/macosx/Makefile b/macosx/Makefile
index 8f313a7a0..42968a147 100644
--- a/macosx/Makefile
+++ b/macosx/Makefile
@@ -34,6 +34,8 @@ CONFIGURE_ARGS = --prefix="$(PREFIX)" --with-libdnet=included --with-libpcap=inc
 # Flags for building universal binaries. See
 # http://developer.apple.com/documentation/Porting/Conceptual/PortingUnix/compiling/chapter_4_section_3.html.
 UNIVERSAL_CONFIGURE_ARGS = --disable-dependency-tracking
+# gcc-4.0 is used to avoid an error with stdarg.h ("No such file or directory")
+# when building against the 10.4u SDK on OS X 10.6.
 UNIVERSAL_CC = gcc-4.0
 UNIVERSAL_CXX = g++-4.0
 UNIVERSAL_CPPFLAGS = -isysroot /Developer/SDKs/MacOSX10.4u.sdk