diff --git a/main.c b/main.c
index 1b99168..ac9d9a3 100644
--- a/main.c
+++ b/main.c
@@ -378,7 +378,10 @@ i2c_end:
 		softi2c_master_stop();
 		if (0 == i2c_rc) {
 			puts("success\r\n");
-			const uint16_t edid_len = edid_length(edid_sink); // get length
+			uint16_t edid_len = edid_length(edid_sink); // get length
+			if (edid_len > 256) { // we only support up to one extension
+				edid_len = 256;
+			}
 			if (edid_len) { // EDID is valid
 				edid_modify(edid_sink); // modify EDID to include firewall indication
 				// compare saved/source and sink EDID