diff --git a/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti2.inc b/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti2.inc
index 82e3142da..d5ddc40a7 100644
--- a/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti2.inc
+++ b/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti2.inc
@@ -81,7 +81,7 @@ OSAL_IRQ_HANDLER(STM32_EXTI2_HANDLER) {
 
   extiGetAndClearGroup1(1U << 2, pr);
 
-  exti_serve_irq(pr, 0);
+  exti_serve_irq(pr, 2);
 
   OSAL_IRQ_EPILOGUE();
 }
diff --git a/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti4.inc b/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti4.inc
index 68c4b60c7..a39e83d4c 100644
--- a/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti4.inc
+++ b/os/hal/ports/STM32/LLD/EXTIv1/stm32_exti4.inc
@@ -81,7 +81,7 @@ OSAL_IRQ_HANDLER(STM32_EXTI4_HANDLER) {
 
   extiGetAndClearGroup1(1U << 4, pr);
 
-  exti_serve_irq(pr, 0);
+  exti_serve_irq(pr, 4);
 
   OSAL_IRQ_EPILOGUE();
 }
diff --git a/readme.txt b/readme.txt
index 688e015cc..b55e5f664 100644
--- a/readme.txt
+++ b/readme.txt
@@ -75,5 +75,7 @@
 
 *** Next ***
 - NEW: Added latency measurement test application:
+- FIX: Fixed error in EXTIv1 ISRs (bug #1077)
+       (backported to 20.3.1)
 - FIX: Fixed problem in chMtxUnlockAllS() (bug #1076)
        (backported to 20.3.1)(backported to 19.1.4)(backported to 18.2.3).