diff --git a/channels/chan_iax2.c b/channels/chan_iax2.c
index 83c33ee0b4..9a65680c8a 100644
--- a/channels/chan_iax2.c
+++ b/channels/chan_iax2.c
@@ -184,7 +184,7 @@ 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 2f3c7851f9..d7d895b251 100644
--- a/include/asterisk/frame.h
+++ b/include/asterisk/frame.h
@@ -267,6 +267,8 @@ 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))
 /*! Raw 16-bit Signed Linear (16000 Hz) PCM */
 #define AST_FORMAT_SLINEAR16	(1 << 15)
 /*! Maximum audio mask */