diff --git a/sys/include/net/gnrc/sixlowpan/frag/rb.h b/sys/include/net/gnrc/sixlowpan/frag/rb.h
index c990ada640..4994044e13 100644
--- a/sys/include/net/gnrc/sixlowpan/frag/rb.h
+++ b/sys/include/net/gnrc/sixlowpan/frag/rb.h
@@ -22,7 +22,9 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include <stdalign.h>
 
+#include "architecture.h"
 #include "net/gnrc/netif/hdr.h"
 #include "net/gnrc/pkt.h"
 #ifdef MODULE_GNRC_SIXLOWPAN_FRAG_SFR
@@ -99,13 +101,14 @@ typedef struct {
      * @brief   The reassembled packet in the packet buffer
      */
     gnrc_pktsnip_t *pkt;
-#if IS_USED(MODULE_GNRC_SIXLOWPAN_FRAG_SFR)
+#if IS_USED(MODULE_GNRC_SIXLOWPAN_FRAG_SFR) || defined(DOXYGEN)
     /**
      * @brief   Bitmap for received fragments
      *
      * @note    Only available with module `gnrc_sixlowpan_frag_sfr` compiled
      *          in.
      */
+    alignas(gnrc_sixlowpan_frag_sfr_bitmap_t)
     BITFIELD(received, SIXLOWPAN_SFR_ACK_BITMAP_SIZE);
     int8_t offset_diff;                         /**< offset change due to
                                                  *   recompression */
diff --git a/sys/net/gnrc/network_layer/sixlowpan/frag/sfr/gnrc_sixlowpan_frag_sfr.c b/sys/net/gnrc/network_layer/sixlowpan/frag/sfr/gnrc_sixlowpan_frag_sfr.c
index 8058a5b545..7b77c12e7a 100644
--- a/sys/net/gnrc/network_layer/sixlowpan/frag/sfr/gnrc_sixlowpan_frag_sfr.c
+++ b/sys/net/gnrc/network_layer/sixlowpan/frag/sfr/gnrc_sixlowpan_frag_sfr.c
@@ -13,6 +13,8 @@
  * @author  Martine Lenders <m.lenders@fu-berlin.de>
  */
 
+#include <stddef.h>
+
 #include "irq.h"
 #include "kernel_defines.h"
 #ifdef MODULE_GNRC_IPV6_NIB
@@ -106,7 +108,7 @@ static gnrc_sixlowpan_frag_sfr_stats_t _stats;
  *
  * @return  A gnrc_sixlowpan_frag_sfr_bitmap_t.
  */
-static inline gnrc_sixlowpan_frag_sfr_bitmap_t *_to_bitmap(uint8_t *bitmap);
+static inline gnrc_sixlowpan_frag_sfr_bitmap_t *_get_bitmap(gnrc_sixlowpan_frag_rb_t *frag_rb);
 
 /**
  * @brief   Checks if fragment represented by a fragment descriptor requested an
@@ -927,7 +929,7 @@ static void _try_reassembly(gnrc_netif_hdr_t *netif_hdr,
                       entry->entry.rb->received[3],
                       entry->entry.base->current_size,
                       entry->entry.base->datagram_size);
-                bitmap = _to_bitmap(entry->entry.rb->received);
+                bitmap = _get_bitmap(entry->entry.rb);
                 if (IS_USED(MODULE_GNRC_SIXLOWPAN_FRAG_SFR_STATS)) {
                     _stats.acks.partly++;
                 }
@@ -1209,9 +1211,14 @@ static void _check_failed_frags(sixlowpan_sfr_ack_t *ack,
 
 /* ====== INTERNAL FUNCTIONS USED BY PUBLIC FUNCTIONS ======
  * ====== AND TO MANIPULATE INTERNAL DATA STRUCTURES  ====== */
-static inline gnrc_sixlowpan_frag_sfr_bitmap_t *_to_bitmap(uint8_t *bitmap)
+static inline gnrc_sixlowpan_frag_sfr_bitmap_t *_get_bitmap(gnrc_sixlowpan_frag_rb_t *frag_rb)
 {
-    return (gnrc_sixlowpan_frag_sfr_bitmap_t *)bitmap;
+    DECLARE_CONSTANT(is_aligned,
+        HAS_ALIGNMENT_OF(offsetof(gnrc_sixlowpan_frag_rb_t, received),
+                         alignof(gnrc_sixlowpan_frag_sfr_bitmap_t)))
+    static_assert(is_aligned,
+                  "gnrc_sixlowpan_frag_rb_t::received must be suitably aligned");
+    return (gnrc_sixlowpan_frag_sfr_bitmap_t *)(uintptr_t)frag_rb->received;
 }
 
 static inline bool _frag_ack_req(_frag_desc_t *frag)
@@ -1394,7 +1401,7 @@ static int _resend_frag(clist_node_t *node, void *fbuf_ptr)
     cur_frag_size = _find_offset_and_copy_rest(data, &pkt, frag_size,
                                                frag_desc->offset);
     /* copy remaining packet snips */
-    cur_frag_size = _copy_pkt_to_frag(data, pkt, frag_size, cur_frag_size);
+    _copy_pkt_to_frag(data, pkt, frag_size, cur_frag_size);
     DEBUG("6lo sfr: resending fragment (retry: %u, tag: %u, X: %i, seq: %u, "
           "frag_size: %u, %s: %u)\n", frag_desc->retries,
           hdr->base.tag, sixlowpan_sfr_rfrag_ack_req(hdr),