diff --git a/sys/contrib/zlib/deflate.c b/sys/contrib/zlib/deflate.c
index 58eabc9959c8..061ad0d66d86 100644
--- a/sys/contrib/zlib/deflate.c
+++ b/sys/contrib/zlib/deflate.c
@@ -189,9 +189,11 @@ local const config configuration_table[10] = {
  * Initialize the hash table (avoiding 64K overflow for 16 bit systems).
  * prev[] will be initialized on the fly.
  */
-#define CLEAR_HASH(s) do { \
-    s->head[s->hash_size-1] = NIL; \
-    zmemzero((Bytef *)s->head, (unsigned)(s->hash_size-1)*sizeof(*s->head)); \
+#define CLEAR_HASH(s) \
+    do { \
+        s->head[s->hash_size-1] = NIL; \
+        zmemzero((Bytef *)s->head, \
+                 (unsigned)(s->hash_size-1)*sizeof(*s->head)); \
     } while (0)
 
 /* ===========================================================================