diff --git a/libs/freetdm/src/include/openzap.h b/libs/freetdm/src/include/openzap.h
index 7e670f14c2..567a0e53eb 100644
--- a/libs/freetdm/src/include/openzap.h
+++ b/libs/freetdm/src/include/openzap.h
@@ -166,6 +166,7 @@
 #define zap_copy_string(x,y,z) strncpy(x, y, z - 1) 
 #define zap_set_string(x,y) strncpy(x, y, sizeof(x)-1) 
 #define zap_strlen_zero(s) (!s || *s == '\0')
+#define zap_strlen_zero_buf(s) (*s == '\0')
 
 
 #define zap_channel_test_feature(obj, flag) ((obj)->features & flag)
diff --git a/libs/freetdm/src/zap_io.c b/libs/freetdm/src/zap_io.c
index 1f07f3af98..8d74f9faf6 100644
--- a/libs/freetdm/src/zap_io.c
+++ b/libs/freetdm/src/zap_io.c
@@ -1698,7 +1698,7 @@ static zap_status_t handle_dtmf(zap_channel_t *zchan, zap_size_t datalen)
 			dblen = sizeof(digits) - 1;
 		}
 
-		if (zap_buffer_read(zchan->gen_dtmf_buffer, digits, dblen) && !zap_strlen_zero(digits)) {
+		if (zap_buffer_read(zchan->gen_dtmf_buffer, digits, dblen) && !zap_strlen_zero_buf(digits)) {
 			zap_log(ZAP_LOG_DEBUG, "%d:%d GENERATE DTMF [%s]\n", zchan->span_id, zchan->chan_id, digits);	
 		
 			for (cur = digits; *cur; cur++) {