diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 4aa88292e2..2f7da5fd23 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -16314,7 +16314,8 @@ static int sip_addheader(struct ast_channel *chan, void *data)
 		no++;
 		snprintf(varbuf, sizeof(varbuf), "_SIPADDHEADER%.2d", no);
 
-		if( (pbx_builtin_getvar_helper(chan, (const char *) varbuf) == (const char *) NULL) )
+		/* Compare without the leading underscore */
+		if( (pbx_builtin_getvar_helper(chan, (const char *) varbuf + 1) == (const char *) NULL) )
 			ok = TRUE;
 	}
 	if (ok) {