diff --git a/Makefile b/Makefile
index 81075c38a2..ed2868ce10 100644
--- a/Makefile
+++ b/Makefile
@@ -110,6 +110,9 @@ include shared.mak
 # Define USE_HOMEBREW_LIBICONV to link against libiconv installed by
 # Homebrew, if present.
 #
+# Define DARWIN_REGEXEC if regexec() in your platform regex library
+# leaks when fed an invalid UTF-8 sequence.
+#
 # Define NO_APPLE_COMMON_CRYPTO if you are building on Darwin/Mac OS X
 # and do not want to use Apple's CommonCrypto library.  This allows you
 # to provide your own OpenSSL library, for example from MacPorts.