diff --git a/main.c b/main.c
index 582d583..9ba3b9d 100644
--- a/main.c
+++ b/main.c
@@ -503,6 +503,7 @@ level pulse on the Hot Plug Detect pin. This pulse shall be at least 100 msec.
 		if (i2c_prog) { // received data over i2c to be programmed
 			if (EDID_PORT->IDR.reg & EDID_PIN) { // EDID switched off
 				puts("I²C prog disabled\r\n");
+				I2C_CR2 &= I2C_CR2_ACK; // NACK next received byte to indicate programming it disabled
 			} else { // EDID programming allowed
 /*
 				puts("I²C prog ");
@@ -525,7 +526,7 @@ level pulse on the Hot Plug Detect pin. This pulse shall be at least 100 msec.
 				if (!(FLASH_IAPSR & FLASH_IAPSR_EOP)) {
 					FLASH_IAPSR &= ~FLASH_IAPSR_DUL; // re-enable write protection
 					LED_PORT->ODR.reg &= ~LED_PIN; // switch LED on to indicate programming failed
-					//I2C_CR2 &= I2C_CR2_ACK; // NACK next received byte
+					I2C_CR2 &= I2C_CR2_ACK; // NACK next received byte to indicate programming error
 					puts("EEPROM byte prog failed\r\n");
 				}
 				FLASH_IAPSR &= ~FLASH_IAPSR_DUL; // re-enable write protection
@@ -564,6 +565,9 @@ void i2c(void) __interrupt(IRQ_I2C) // auto wakeup
 		} else { // received data byte
 			i2c_prog = true; // notify main loop data needs to be programmed
 		}
+		if (EDID_PORT->IDR.reg & EDID_PIN) { // EDID programming is not enabled
+			I2C_CR2 &= I2C_CR2_ACK; // NACK next received byte to indicate programming it disabled
+		}
 	}
 	if (sr1 & I2C_SR1_STOPF) { // stop received
 		I2C_CR2 |= I2C_CR2_ACK; // this is just to clear the flag