diff --git a/extensions/Makefile.in b/extensions/Makefile.in
index 052903c20..5d2ee63db 100644
--- a/extensions/Makefile.in
+++ b/extensions/Makefile.in
@@ -27,6 +27,7 @@ INCLUDES	= -I. -I../include -I../libratbox/include $(SSL_INCLUDES)
 CPPFLAGS	= ${INCLUDES} @CPPFLAGS@
 
 SRCS =                          \
+  chm_operonly_compat.c		\
   chm_quietunreg_compat.c	\
   chm_sslonly_compat.c		\
   createauthonly.c		\
diff --git a/extensions/chm_operonly_compat.c b/extensions/chm_operonly_compat.c
new file mode 100644
index 000000000..f30104eb7
--- /dev/null
+++ b/extensions/chm_operonly_compat.c
@@ -0,0 +1,63 @@
+/*
+ * Treat cmode +-O as +-iI $o.
+ */
+
+#include "stdinc.h"
+#include "modules.h"
+#include "client.h"
+#include "hook.h"
+#include "ircd.h"
+
+/* XXX prototypes */
+void chm_ban(struct Client *source_p, struct Channel *chptr,
+	int alevel, int parc, int *parn,
+	const char **parv, int *errors, int dir, char c, long mode_type);
+void chm_nosuch(struct Client *source_p, struct Channel *chptr,
+	int alevel, int parc, int *parn,
+	const char **parv, int *errors, int dir, char c, long mode_type);
+void chm_simple(struct Client *source_p, struct Channel *chptr,
+	int alevel, int parc, int *parn,
+	const char **parv, int *errors, int dir, char c, long mode_type);
+/* end yucky prototypes */
+
+static int _modinit(void);
+static void _moddeinit(void);
+static void chm_operonly(struct Client *source_p, struct Channel *chptr,
+	int alevel, int parc, int *parn,
+	const char **parv, int *errors, int dir, char c, long mode_type);
+
+DECLARE_MODULE_AV1(chm_operonly_compat, _modinit, _moddeinit, NULL, NULL, NULL, "$Revision$");
+
+static int
+_modinit(void)
+{
+	chmode_table['O'].set_func = chm_operonly;
+	chmode_table['O'].mode_type = 0;
+
+	return 0;
+}
+
+static void
+_moddeinit(void)
+{
+	chmode_table['O'].set_func = chm_nosuch;
+	chmode_table['O'].mode_type = 0;
+}
+
+static void
+chm_operonly(struct Client *source_p, struct Channel *chptr,
+	int alevel, int parc, int *parn,
+	const char **parv, int *errors, int dir, char c, long mode_type)
+{
+	int newparn = 0;
+	const char *newparv[] = { "$o" };
+
+	if (MyClient(source_p)) {
+		chm_simple(source_p, chptr, alevel, parc, parn, parv,
+				errors, dir, 'i', MODE_INVITEONLY);
+		chm_ban(source_p, chptr, alevel, 1, &newparn, newparv,
+				errors, dir, 'I', CHFL_INVEX);
+	} else
+		chm_nosuch(source_p, chptr, alevel, parc, parn, parv,
+				errors, dir, c, mode_type);
+}