diff --git a/pkg/littlefs/fs/littlefs_fs.c b/pkg/littlefs/fs/littlefs_fs.c
index 7f6840eb8e..6f23c90676 100644
--- a/pkg/littlefs/fs/littlefs_fs.c
+++ b/pkg/littlefs/fs/littlefs_fs.c
@@ -349,8 +349,8 @@ static ssize_t _write(vfs_file_t *filp, const void *src, size_t nbytes)
 
     mutex_lock(&fs->lock);
 
-    DEBUG("littlefs: write: filp=%p, fp=%p, src=%p, nbytes=%u\n",
-          (void *)filp, (void *)fp, (void *)src, (unsigned)nbytes);
+    DEBUG("littlefs: write: filp=%p, fp=%p, src=%p, nbytes=%" PRIuSIZE "\n",
+          (void *)filp, (void *)fp, (void *)src, nbytes);
 
     ssize_t ret = lfs_file_write(&fs->fs, fp, src, nbytes);
     mutex_unlock(&fs->lock);
@@ -365,8 +365,8 @@ static ssize_t _read(vfs_file_t *filp, void *dest, size_t nbytes)
 
     mutex_lock(&fs->lock);
 
-    DEBUG("littlefs: read: filp=%p, fp=%p, dest=%p, nbytes=%u\n",
-          (void *)filp, (void *)fp, (void *)dest, (unsigned)nbytes);
+    DEBUG("littlefs: read: filp=%p, fp=%p, dest=%p, nbytes=%" PRIuSIZE "\n",
+          (void *)filp, (void *)fp, (void *)dest, nbytes);
 
     ssize_t ret = lfs_file_read(&fs->fs, fp, dest, nbytes);
     mutex_unlock(&fs->lock);
diff --git a/pkg/littlefs2/fs/littlefs2_fs.c b/pkg/littlefs2/fs/littlefs2_fs.c
index 6cd651b68e..d2968aa6f6 100644
--- a/pkg/littlefs2/fs/littlefs2_fs.c
+++ b/pkg/littlefs2/fs/littlefs2_fs.c
@@ -354,8 +354,8 @@ static ssize_t _write(vfs_file_t *filp, const void *src, size_t nbytes)
 
     mutex_lock(&fs->lock);
 
-    DEBUG("littlefs: write: filp=%p, fp=%p, src=%p, nbytes=%u\n",
-          (void *)filp, (void *)fp, (void *)src, (unsigned)nbytes);
+    DEBUG("littlefs: write: filp=%p, fp=%p, src=%p, nbytes=%" PRIuSIZE "\n",
+          (void *)filp, (void *)fp, (void *)src, nbytes);
 
     ssize_t ret = lfs_file_write(&fs->fs, fp, src, nbytes);
     mutex_unlock(&fs->lock);
@@ -370,8 +370,8 @@ static ssize_t _read(vfs_file_t *filp, void *dest, size_t nbytes)
 
     mutex_lock(&fs->lock);
 
-    DEBUG("littlefs: read: filp=%p, fp=%p, dest=%p, nbytes=%u\n",
-          (void *)filp, (void *)fp, (void *)dest, (unsigned)nbytes);
+    DEBUG("littlefs: read: filp=%p, fp=%p, dest=%p, nbytes=%" PRIuSIZE "\n",
+          (void *)filp, (void *)fp, (void *)dest, nbytes);
 
     ssize_t ret = lfs_file_read(&fs->fs, fp, dest, nbytes);
     mutex_unlock(&fs->lock);
diff --git a/pkg/tinydtls/contrib/sock_dtls.c b/pkg/tinydtls/contrib/sock_dtls.c
index f5fdc0d6aa..960c30a430 100644
--- a/pkg/tinydtls/contrib/sock_dtls.c
+++ b/pkg/tinydtls/contrib/sock_dtls.c
@@ -118,7 +118,7 @@ static int _write(struct dtls_context_t *ctx, session_t *session, uint8_t *buf,
     ssize_t res = sock_udp_send(sock->udp_sock, buf, len, &remote);
 
     if (res < 0) {
-        DEBUG("sock_dtls: failed to send DTLS record: %d\n", (int)res);
+        DEBUG("sock_dtls: failed to send DTLS record: %" PRIdSIZE "\n", res);
     }
     return res;
 }
@@ -793,7 +793,7 @@ ssize_t sock_dtls_recv_aux(sock_dtls_t *sock, sock_dtls_session_t *remote,
         res = sock_udp_recv_aux(sock->udp_sock, data, max_len, timeout,
                                 &ep, (sock_udp_aux_rx_t *)aux);
         if (res <= 0) {
-            DEBUG("sock_dtls: error receiving UDP packet: %d\n", (int)res);
+            DEBUG("sock_dtls: error receiving UDP packet: %" PRIdSIZE "\n", res);
             return res;
         }
 
@@ -858,7 +858,7 @@ ssize_t sock_dtls_recv_buf_aux(sock_dtls_t *sock, sock_dtls_session_t *remote,
             continue;
         }
         if (res < 0) {
-            DEBUG("sock_dtls: error receiving UDP packet: %d\n", (int)res);
+            DEBUG("sock_dtls: error receiving UDP packet: %" PRIdSIZE "\n", res);
             return res;
         }
 
@@ -974,7 +974,7 @@ void _udp_cb(sock_udp_t *udp_sock, sock_async_flags_t flags, void *ctx)
         ssize_t res = sock_udp_recv_buf(udp_sock, &data, &data_ctx, 0,
                                         &remote_ep);
         if (res <= 0) {
-            DEBUG("sock_dtls: error receiving UDP packet: %d\n", (int)res);
+            DEBUG("sock_dtls: error receiving UDP packet: %" PRIdSIZE "\n", res);
             return;
         }
 
diff --git a/pkg/tinyvcdiff/contrib/tinyvcdiff_mtd/mtd.c b/pkg/tinyvcdiff/contrib/tinyvcdiff_mtd/mtd.c
index 5ad45cdfdb..0623c66fd4 100644
--- a/pkg/tinyvcdiff/contrib/tinyvcdiff_mtd/mtd.c
+++ b/pkg/tinyvcdiff/contrib/tinyvcdiff_mtd/mtd.c
@@ -6,6 +6,7 @@
  * directory for more details.
  */
 
+#include "architecture.h"
 #include "vcdiff_mtd.h"
 #include "assert.h"
 #include <string.h>
@@ -71,7 +72,7 @@ static int _align_write (vcdiff_mtd_t *mtd, uint8_t **src, size_t *len)
     mtd->offset += copy_len;
     *len -= copy_len;
     *src += copy_len;
-    DEBUG("_align_write: buffered %zuB for alignment\n", copy_len);
+    DEBUG("_align_write: buffered %" PRIuSIZE "B for alignment\n", copy_len);
 
     if (alignment_offset < CONFIG_TINYVCDIFF_MTD_WRITE_SIZE) {
         /* we haven't collected enough bytes, yet */
@@ -99,7 +100,7 @@ static int _write (void *dev, uint8_t *src, size_t offset, size_t len)
 
     assert(offset == mtd->offset);
 
-    DEBUG("_write: 0x%zx + %zuB\n", mtd->offset, len);
+    DEBUG("_write: 0x%" PRIxSIZE " + %" PRIuSIZE "B\n", mtd->offset, len);
 
     /* align writes */
     rc = _align_write(dev, &src, &len);
@@ -132,7 +133,7 @@ static int _write (void *dev, uint8_t *src, size_t offset, size_t len)
     /* copy remaining bytes into write_buffer */
     memcpy(mtd->write_buffer, src, len);
     mtd->offset += len;
-    DEBUG("_write: buffered %zuB for alignment\n", len);
+    DEBUG("_write: buffered %" PRIuSIZE "B for alignment\n", len);
 
     return rc;
 }
@@ -150,7 +151,7 @@ static int _flush (void *dev)
         return 0;
     }
 
-    DEBUG("_flush: write last %zuB\n", alignment_offset);
+    DEBUG("_flush: write last %" PRIuSIZE "B\n", alignment_offset);
 
     /* get present bytes from MTD to pad alignment */
     rc = mtd_read_page(mtd->dev, buf, 0, mtd->offset - alignment_offset,
diff --git a/pkg/tlsf/contrib/tlsf-malloc.c b/pkg/tlsf/contrib/tlsf-malloc.c
index 4683065b3d..4bc65a8428 100644
--- a/pkg/tlsf/contrib/tlsf-malloc.c
+++ b/pkg/tlsf/contrib/tlsf-malloc.c
@@ -46,7 +46,8 @@ tlsf_t _tlsf_get_global_control(void)
 
 void tlsf_size_walker(void* ptr, size_t size, int used, void* user)
 {
-    printf("\t%p %s size: %u (%p)\n", ptr, used ? "used" : "free", (unsigned int)size, ptr);
+    printf("\t%p %s size: %" PRIuSIZE " (%p)\n", ptr, used ? "used" : "free",
+           size, ptr);
 
     if (used) {
         ((tlsf_size_container_t *)user)->used += (unsigned int)size;
diff --git a/pkg/wakaama/contrib/lwm2m_client.c b/pkg/wakaama/contrib/lwm2m_client.c
index be55aceff6..48a22260b7 100644
--- a/pkg/wakaama/contrib/lwm2m_client.c
+++ b/pkg/wakaama/contrib/lwm2m_client.c
@@ -182,7 +182,7 @@ static void *_lwm2m_client_run(void *arg)
             lwm2m_client_connection_t *conn = lwm2m_client_connection_find(
                                             _client_data->conn_list, &remote);
             if (conn) {
-                DEBUG("lwm2m_connection_handle_packet(%i)\n", (int)rcv_len);
+                DEBUG("lwm2m_connection_handle_packet(%" PRIiSIZE ")\n", rcv_len);
                 int result = lwm2m_connection_handle_packet(conn, rcv_buf,
                                                             rcv_len,
                                                             _client_data);
@@ -196,10 +196,10 @@ static void *_lwm2m_client_run(void *arg)
         }
         else if ((rcv_len < 0) &&
                  ((rcv_len != -EAGAIN) && (rcv_len != -ETIMEDOUT))) {
-            DEBUG("Unexpected sock_udp_recv error code %i\n", (int)rcv_len);
+            DEBUG("Unexpected sock_udp_recv error code %" PRIiSIZE "\n", rcv_len);
         }
         else {
-            DEBUG("UDP error code: %i\n", (int)rcv_len);
+            DEBUG("UDP error code: %" PRIiSIZE "\n", rcv_len);
         }
     }
     return NULL;
diff --git a/pkg/wakaama/contrib/lwm2m_client_connection.c b/pkg/wakaama/contrib/lwm2m_client_connection.c
index 613cd166c6..4090902f00 100644
--- a/pkg/wakaama/contrib/lwm2m_client_connection.c
+++ b/pkg/wakaama/contrib/lwm2m_client_connection.c
@@ -214,7 +214,7 @@ static int _connection_send(lwm2m_client_connection_t *conn, uint8_t *buffer,
     ssize_t sent_bytes = sock_udp_send(&(client_data->sock), buffer,
                                        buffer_size, &(conn->remote));
     if (sent_bytes <= 0) {
-        DEBUG("[_connection_send] Could not send UDP packet: %i\n", (int)sent_bytes);
+        DEBUG("[_connection_send] Could not send UDP packet: %" PRIiSIZE "\n", sent_bytes);
         return -1;
     }
     conn->last_send = lwm2m_gettime();
diff --git a/pkg/wakaama/contrib/lwm2m_platform.c b/pkg/wakaama/contrib/lwm2m_platform.c
index 7a48d4eae0..0097398be5 100644
--- a/pkg/wakaama/contrib/lwm2m_platform.c
+++ b/pkg/wakaama/contrib/lwm2m_platform.c
@@ -50,7 +50,7 @@ typedef struct {
 
  static void _tlsf_size_walker(void* ptr, size_t size, int used, void* user)
 {
-    printf("\t%p %s size: %u (%p)\n", ptr, used ? "used" : "free", (unsigned int)size, ptr);
+    printf("\t%p %s size: %" PRIuSIZE " (%p)\n", ptr, used ? "used" : "free", size, ptr);
 
      if (used) {
         ((_tlsf_size_container_t *)user)->used += (unsigned int)size;