diff --git a/os/ports/cosmic/STM8/chcore.h b/os/ports/cosmic/STM8/chcore.h
index 2a351039c..b65829edc 100644
--- a/os/ports/cosmic/STM8/chcore.h
+++ b/os/ports/cosmic/STM8/chcore.h
@@ -101,6 +101,7 @@ typedef void (*stm8func_t)(void);
  */
 struct extctx {
   uint8_t       _next;
+  uint8_t       c_lreg[4];
   uint8_t       c_y[3];
   uint8_t       c_x[3];
   uint8_t       cc;
@@ -225,7 +226,7 @@ struct stm8_startctx {
  * @note    @p id can be a function name or a vector number depending on the
  *          port implementation.
  */
-#define PORT_IRQ_HANDLER(id) @far @interrupt void vector##id(void)
+#define PORT_IRQ_HANDLER(id) @far @interrupt @svlreg void vector##id(void)
 
 /**
  * @brief   Port-related initialization code.
diff --git a/readme.txt b/readme.txt
index 4fb33f120..35a41ea38 100644
--- a/readme.txt
+++ b/readme.txt
@@ -79,6 +79,7 @@
 *****************************************************************************
 
 *** 2.4.3 ***
+- FIX: Fixed STM8L, cosmic compiler: c_lreg not saved (bug 3566342).
 - FIX: Fixed anomaly in USB enumeration (bug 3565325).
 - FIX: Fixed problem with lwIP statistics (bug 3564134).
 - FIX: Fixed packed structures macros not functional in IAR and RVCT port