diff --git a/channels/chan_iax2.c b/channels/chan_iax2.c
index 82afa17e9b..25c227c757 100644
--- a/channels/chan_iax2.c
+++ b/channels/chan_iax2.c
@@ -175,7 +175,7 @@ static int defaultsockfd = -1;
 int (*iax2_regfunk)(const char *username, int onoff) = NULL;
 
 /* Ethernet, etc */
-#define IAX_CAPABILITY_FULLBANDWIDTH 	0xFFFF
+#define IAX_CAPABILITY_FULLBANDWIDTH 	(0xFFFF & ~AST_FORMAT_AUDIO_UNDEFINED)
 /* T1, maybe ISDN */
 #define IAX_CAPABILITY_MEDBANDWIDTH 	(IAX_CAPABILITY_FULLBANDWIDTH & 	\
 					 ~AST_FORMAT_SLINEAR &			\
diff --git a/include/asterisk/frame.h b/include/asterisk/frame.h
index 6ee131eb2e..34cf11a03a 100644
--- a/include/asterisk/frame.h
+++ b/include/asterisk/frame.h
@@ -260,6 +260,8 @@ extern struct ast_frame ast_null_frame;
 #define AST_FORMAT_G726		(1 << 11)
 /*! G.722 */
 #define AST_FORMAT_G722		(1 << 12)
+/*! Unsupported audio bits */
+#define AST_FORMAT_AUDIO_UNDEFINED	((1 << 13) | (1 << 14) | (1 << 15))
 /*! Maximum audio format */
 #define AST_FORMAT_MAX_AUDIO	(1 << 15)
 /*! Maximum audio mask */