diff --git a/os/hal/ports/STM32/LLD/CANv1/hal_can_lld.c b/os/hal/ports/STM32/LLD/CANv1/hal_can_lld.c
index 09dbac7f0..d0a25fb77 100644
--- a/os/hal/ports/STM32/LLD/CANv1/hal_can_lld.c
+++ b/os/hal/ports/STM32/LLD/CANv1/hal_can_lld.c
@@ -162,14 +162,13 @@ static void can_lld_set_filters(CANDriver* canp,
 #endif
     canp->can->FM1R = 0;
     canp->can->FFA1R = 0;
-#if STM32_CAN_USE_CAN2
-    if(canp == &CAND1) {
-      canp->can->FS1R = 1 | (1 << can2sb);
-      canp->can->FA1R = 1 | (1 << can2sb);
-    }
-#else
     canp->can->FS1R = 1;
     canp->can->FA1R = 1;
+#if STM32_CAN_USE_CAN2
+    if(canp == &CAND1) {
+      canp->can->FS1R |= 1 << can2sb;
+      canp->can->FA1R |= 1 << can2sb;
+    }
 #endif
   }
   canp->can->FMR &= ~CAN_FMR_FINIT;
diff --git a/readme.txt b/readme.txt
index 959871b00..069bdb27c 100644
--- a/readme.txt
+++ b/readme.txt
@@ -93,6 +93,8 @@
        dependencies and configuration directories. This makes possible
        to have multiple non-conflicting makefiles in the same project.
        Updated the various platform.mk implementing "smart build" mode.
+- HAL: Fixed invalid STM32 CAN3 filters initialization (bug #878)
+       (backported to 17.6.1).
 - HAL: Fixed missing CAN definitions in STM32L432 registry entry (bug #877)
        (backported to 17.6.1).
 - HAL: Fixed missing STM32_TIM_MAX_CHANNELS definition in STM32L0 registry