diff --git a/lib/nghttp2_hd.c b/lib/nghttp2_hd.c
index 5e869315..6d54e91d 100644
--- a/lib/nghttp2_hd.c
+++ b/lib/nghttp2_hd.c
@@ -1891,7 +1891,7 @@ ssize_t nghttp2_hd_inflate_hd_nv(nghttp2_hd_inflater *inflater,
         rv = NGHTTP2_ERR_HEADER_COMP;
         goto fail;
       }
-    /* fall through */
+      __attribute__((fallthrough));
     case NGHTTP2_HD_STATE_INFLATE_START:
     case NGHTTP2_HD_STATE_OPCODE:
       if ((*in & 0xe0u) == 0x20u) {
@@ -2001,7 +2001,7 @@ ssize_t nghttp2_hd_inflate_hd_nv(nghttp2_hd_inflater *inflater,
       inflater->left = 0;
       inflater->shift = 0;
       DEBUGF("inflatehd: huffman encoded=%d\n", inflater->huffman_encoded != 0);
-    /* Fall through */
+      __attribute__((fallthrough));
     case NGHTTP2_HD_STATE_NEWNAME_READ_NAMELEN:
       rfin = 0;
       rv = hd_inflate_read_len(inflater, &rfin, in, last, 7, NGHTTP2_HD_MAX_NV);
@@ -2085,7 +2085,7 @@ ssize_t nghttp2_hd_inflate_hd_nv(nghttp2_hd_inflater *inflater,
       inflater->left = 0;
       inflater->shift = 0;
       DEBUGF("inflatehd: huffman encoded=%d\n", inflater->huffman_encoded != 0);
-    /* Fall through */
+      __attribute__((fallthrough));
     case NGHTTP2_HD_STATE_READ_VALUELEN:
       rfin = 0;
       rv = hd_inflate_read_len(inflater, &rfin, in, last, 7, NGHTTP2_HD_MAX_NV);
diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index 36f1179f..f007dbf4 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -2644,10 +2644,10 @@ static int session_after_frame_sent1(nghttp2_session *session) {
     case NGHTTP2_HCAT_PUSH_RESPONSE:
       stream->flags = (uint8_t)(stream->flags & ~NGHTTP2_STREAM_FLAG_PUSH);
       ++session->num_outgoing_streams;
-    /* Fall through */
+      __attribute__((fallthrough));
     case NGHTTP2_HCAT_RESPONSE:
       stream->state = NGHTTP2_STREAM_OPENED;
-    /* Fall through */
+      __attribute__((fallthrough));
     case NGHTTP2_HCAT_HEADERS:
       if (frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
         nghttp2_stream_shutdown(stream, NGHTTP2_SHUT_WR);
@@ -5456,7 +5456,7 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
 
       iframe->state = NGHTTP2_IB_READ_HEAD;
 
-    /* Fall through */
+      __attribute__((fallthrough));
     case NGHTTP2_IB_READ_HEAD: {
       int on_begin_frame_called = 0;