diff --git a/lib/zlib/infback.c b/lib/zlib/infback.c
index 6f4279439..fac20afa1 100644
--- a/lib/zlib/infback.c
+++ b/lib/zlib/infback.c
@@ -477,7 +477,7 @@ void FAR *out_desc;
             }
             Tracev((stderr, "inflate:       codes ok\n"));
             state->mode = LEN;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
 
         case LEN:
             /* use inflate_fast() if we have enough input and output */
diff --git a/lib/zlib/inflate.c b/lib/zlib/inflate.c
index b623ba707..86a0f3d79 100644
--- a/lib/zlib/inflate.c
+++ b/lib/zlib/inflate.c
@@ -740,7 +740,7 @@ int flush;
                 CRC2(state->check, hold);
             INITBITS();
             state->mode = EXLEN;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case EXLEN:
             if (state->flags & 0x0400) {
                 NEEDBITS(16);
@@ -754,7 +754,7 @@ int flush;
             else if (state->head != Z_NULL)
                 state->head->extra = Z_NULL;
             state->mode = EXTRA;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case EXTRA:
             if (state->flags & 0x0400) {
                 copy = state->length;
@@ -777,7 +777,7 @@ int flush;
             }
             state->length = 0;
             state->mode = NAME;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case NAME:
             if (state->flags & 0x0800) {
                 if (have == 0) goto inf_leave;
@@ -799,7 +799,7 @@ int flush;
                 state->head->name = Z_NULL;
             state->length = 0;
             state->mode = COMMENT;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case COMMENT:
             if (state->flags & 0x1000) {
                 if (have == 0) goto inf_leave;
@@ -820,7 +820,7 @@ int flush;
             else if (state->head != Z_NULL)
                 state->head->comment = Z_NULL;
             state->mode = HCRC;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case HCRC:
             if (state->flags & 0x0200) {
                 NEEDBITS(16);
@@ -844,7 +844,7 @@ int flush;
             strm->adler = state->check = ZSWAP32(hold);
             INITBITS();
             state->mode = DICT;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case DICT:
             if (state->havedict == 0) {
                 RESTORE();
@@ -852,10 +852,10 @@ int flush;
             }
             strm->adler = state->check = adler32(0L, Z_NULL, 0);
             state->mode = TYPE;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case TYPE:
             if (flush == Z_BLOCK || flush == Z_TREES) goto inf_leave;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case TYPEDO:
             if (state->last) {
                 BYTEBITS();
@@ -906,10 +906,10 @@ int flush;
             INITBITS();
             state->mode = COPY_;
             if (flush == Z_TREES) goto inf_leave;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case COPY_:
             state->mode = COPY;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case COPY:
             copy = state->length;
             if (copy) {
@@ -1049,10 +1049,10 @@ int flush;
             Tracev((stderr, "inflate:       codes ok\n"));
             state->mode = LEN_;
             if (flush == Z_TREES) goto inf_leave;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case LEN_:
             state->mode = LEN;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case LEN:
             if (have >= 6 && left >= 258) {
                 RESTORE();
@@ -1102,7 +1102,7 @@ int flush;
             }
             state->extra = (unsigned)(here.op) & 15;
             state->mode = LENEXT;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case LENEXT:
             if (state->extra) {
                 NEEDBITS(state->extra);
@@ -1113,7 +1113,7 @@ int flush;
             Tracevv((stderr, "inflate:         length %u\n", state->length));
             state->was = state->length;
             state->mode = DIST;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case DIST:
             for (;;) {
                 here = state->distcode[BITS(state->distbits)];
@@ -1141,7 +1141,7 @@ int flush;
             state->offset = (unsigned)here.val;
             state->extra = (unsigned)(here.op) & 15;
             state->mode = DISTEXT;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case DISTEXT:
             if (state->extra) {
                 NEEDBITS(state->extra);
@@ -1158,7 +1158,7 @@ int flush;
 #endif
             Tracevv((stderr, "inflate:         distance %u\n", state->offset));
             state->mode = MATCH;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case MATCH:
             if (left == 0) goto inf_leave;
             copy = out - left;
@@ -1234,7 +1234,7 @@ int flush;
             }
 #ifdef GUNZIP
             state->mode = LENGTH;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case LENGTH:
             if (state->wrap && state->flags) {
                 NEEDBITS(32);
@@ -1248,7 +1248,7 @@ int flush;
             }
 #endif
             state->mode = DONE;
-	    /* FALLTHROUGH */
+	    ZFALLTHROUGH;
         case DONE:
             ret = Z_STREAM_END;
             goto inf_leave;
diff --git a/lib/zlib/zconf.h.in b/lib/zlib/zconf.h.in
index 5e6c4a2e8..0b6bd5360 100644
--- a/lib/zlib/zconf.h.in
+++ b/lib/zlib/zconf.h.in
@@ -9,6 +9,7 @@
 #define ZCONF_H
 
 /* The following four defines are enabled by sudo's configure script. */
+#undef HAVE_FALLTHROUGH_ATTRIBUTE
 #undef HAVE_DSO_VISIBILITY
 #undef HAVE_MEMCPY
 #undef HAVE_UNISTD_H
@@ -30,6 +31,12 @@
 # endif
 #endif
 
+#ifdef HAVE_FALLTHROUGH_ATTRIBUTE
+# define ZFALLTHROUGH	__attribute__((__fallthrough__))
+#else
+# define ZFALLTHROUGH	do { } while (0)
+#endif
+
 /*
  * If you *really* need a unique prefix for all types and library functions,
  * compile with -DZ_PREFIX. The "standard" zlib should be compiled without it.