diff --git a/os/ports/IAR/ARMCMx/chtypes.h b/os/ports/IAR/ARMCMx/chtypes.h
index 36e24e5c7..221b2819b 100644
--- a/os/ports/IAR/ARMCMx/chtypes.h
+++ b/os/ports/IAR/ARMCMx/chtypes.h
@@ -61,15 +61,14 @@ typedef int32_t         cnt_t;          /**< Resources counter.             */
 
 /**
  * @brief   Packed structure modifier (within).
- * @note    It uses the "packed" GCC attribute.
+ * @note    Empty in this port.
  */
-#define PACK_STRUCT_STRUCT __attribute__((packed))
+#define PACK_STRUCT_STRUCT
 
 /**
  * @brief   Packed structure modifier (before).
- * @note    Empty in this port.
  */
-#define PACK_STRUCT_BEGIN
+#define PACK_STRUCT_BEGIN __packed
 
 /**
  * @brief   Packed structure modifier (after).
diff --git a/os/ports/RVCT/ARMCMx/chtypes.h b/os/ports/RVCT/ARMCMx/chtypes.h
index b9baf2502..8619dcdfe 100644
--- a/os/ports/RVCT/ARMCMx/chtypes.h
+++ b/os/ports/RVCT/ARMCMx/chtypes.h
@@ -61,15 +61,15 @@ typedef int32_t         cnt_t;          /**< Resources counter.             */
 
 /**
  * @brief   Packed structure modifier (within).
- * @note    It uses the "packed" GCC attribute.
+ * @note    Empty in this port.
  */
-#define PACK_STRUCT_STRUCT __attribute__((packed))
+#define PACK_STRUCT_STRUCT
 
 /**
  * @brief   Packed structure modifier (before).
  * @note    Empty in this port.
  */
-#define PACK_STRUCT_BEGIN
+#define PACK_STRUCT_BEGIN __packed
 
 /**
  * @brief   Packed structure modifier (after).
diff --git a/readme.txt b/readme.txt
index 92f9faeae..b02ff4520 100644
--- a/readme.txt
+++ b/readme.txt
@@ -82,6 +82,8 @@
 *****************************************************************************
 
 *** 2.5.0 ***
+- FIX: Fixed packed structures macros not functional in IAR and RVCT port
+  (bug 3561279)(backported to 2.4.3 and 2.2.10).
 - FIX: Fixed Problem in FatFs demos related to LFN (bug 3560980)(backported
   to 2.4.3 and 2.2.10).
 - FIX: Fixed problem in STM32 DMA1 stream1 IRQ handler (bug 3538468)