diff --git a/main.c b/main.c
index 0c055e2..83416b5 100644
--- a/main.c
+++ b/main.c
@@ -105,18 +105,16 @@ static bool checksum_ok(const uint8_t* data, uint16_t length)
 	return (0 == checksum);
 }
 
-// return if the current EDID is valid
+// return if the current EDID its length (including extensions), or 0 if invalid
 /* from HDMI 1.3a specification
  * All Sinks shall contain an CEA-861-D compliant E-EDID data structure.
- * A Source shall read the EDID 1.3 and first CEA Extension to determine the capabilities supported
-by the Sink.
- * The first 128 bytes of the E-EDID shall contain an EDID 1.3 structure. The contents of this
-structure shall also meet the requirements of CEA-861-D.
+ * A Source shall read the EDID 1.3 and first CEA Extension to determine the capabilities supported by the Sink.
+ * The first 128 bytes of the E-EDID shall contain an EDID 1.3 structure. The contents of this structure shall also meet the requirements of CEA-861-D.
  *
  * HDMI 2.1 uses CTA-861-G
  * this uses EDID 1.4 structure
  * EDID 1.3/1.4 is 128 bytes long, and can point to 128 bytes extension
- * EDID 2.0 with its 256 bytes does not seem to be used in HDMI at all
+ * EDID 2.0 with its 256 bytes does not seem to be used in HDMI at all (and is deprecated, replaced by E-EDID)
  * DisplayID with its variable-length structure meant to replace E-EDID only seems to be used in DisplayPort
  */
 static uint16_t edid_length(const uint8_t* edid)
@@ -129,28 +127,28 @@ static uint16_t edid_length(const uint8_t* edid)
 	}
 
 	if (1 == edid[18]) { // EDID 1.3/1.4 128-byte structure
-		if (checksum_ok(&edid[0], 128)) {
-			if (0 == edid[126]) { // no extension
-				puts("128 bytes\r\n");
-				return 128;
-			} else { // extension available
-				// the usual extension is CEA EDID Timing Extension (with extension tag 02), but we allow others
-				// no idea how more than 1 extension is supported
-				if (checksum_ok(&edid[128], 128)) {
-					puts("256 bytes (with extension)\r\n");
-					return 256;
-				} else {
+		if (checksum_ok(&edid[0], 128)) { // ensure checksum of base EDID is ok
+			const uint16_t length = 128 + (1 + edid[126]) * 128; // get length with all extensions
+			puts("(v1.4 ");
+			putn(edid[126]  / 100);
+			putn((edid[126]  / 10) % 10);
+			putn(edid[126] % 10);
+			puts(" extension) ");
+			for (uint16_t i = 128; i < length && i < 256; i += 128) { // verify checksum of each extension (we actually only support one extension)
+				if (!checksum_ok(&edid[i], 128)) {
 					puts("extension CRC error\r\n");
 					return 0; // EDID is broken
 				}
 			}
+			puts("CRC ok\r\n");
+			return length;
 		} else {
-			puts("CRC error\r\n");
+			puts("base CRC error\r\n");
 			return 0;
 		}
 	} else if (2 == edid[18]) { // EDID 2.0 256-byte structure
 		if (checksum_ok(&edid[0], 256)) {
-			puts("256 bytes (no extension)\r\n");
+			puts("(v2) CRC ok\r\n");
 			return 256;
 		} else {
 			puts("CRC error\r\n");