diff --git a/src/base64.h b/src/base64.h
index b63777f0..2e3d7d8b 100644
--- a/src/base64.h
+++ b/src/base64.h
@@ -19,7 +19,7 @@ size_t li_base64_enc(char* restrict out, size_t out_length, const unsigned char*
 #define li_to_base64(out, out_length, in, in_length, charset) \
         li_base64_enc((out), (out_length), (in), (in_length), (charset), 1)
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 char* buffer_append_base64_enc(buffer *out, const unsigned char* in, size_t in_length, base64_charset charset, int pad);
 
diff --git a/src/buffer.c b/src/buffer.c
index bad5f743..15ae282e 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -56,7 +56,7 @@ void buffer_move(buffer * restrict b, buffer * restrict src) {
 /* make sure buffer is at least "size" big + 1 for '\0'. keep old data */
 __attribute_cold__
 __attribute_noinline__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static char* buffer_realloc(buffer * const restrict b, const size_t len) {
     #define BUFFER_PIECE_SIZE 64uL  /*(must be power-of-2)*/
@@ -78,7 +78,7 @@ static char* buffer_realloc(buffer * const restrict b, const size_t len) {
 
 __attribute_cold__
 __attribute_noinline__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static char* buffer_alloc_replace(buffer * const restrict b, const size_t size) {
     /*(discard old data so realloc() does not copy)*/
@@ -103,7 +103,7 @@ char* buffer_string_prepare_copy(buffer * const b, const size_t size) {
 
 __attribute_cold__
 __attribute_noinline__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static char* buffer_string_prepare_append_resize(buffer * const restrict b, const size_t size) {
     if (b->used < 2) {  /* buffer_is_blank(b) */
@@ -300,7 +300,7 @@ void buffer_append_uint_hex_lc(buffer *b, uintmax_t value) {
 	}
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static char* utostr(char buf[LI_ITOSTRING_LENGTH], uintmax_t val) {
 	char *cur = buf+LI_ITOSTRING_LENGTH;
@@ -313,7 +313,7 @@ static char* utostr(char buf[LI_ITOSTRING_LENGTH], uintmax_t val) {
 	return cur;
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static char* itostr(char buf[LI_ITOSTRING_LENGTH], intmax_t val) {
 	/* absolute value not defined for INTMAX_MIN, but can take absolute
diff --git a/src/buffer.h b/src/buffer.h
index facabb89..5f13b846 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -33,7 +33,7 @@ __attribute_malloc__
 __attribute_returns_nonnull__
 buffer* buffer_init(void);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 buffer* buffer_init_buffer(const buffer *src);
 
@@ -43,7 +43,7 @@ buffer* buffer_init_string(const char *str); /* str can  be NULL */
 void buffer_free(buffer *b); /* b can be NULL */
 
 /* reset b. if NULL != b && NULL != src, move src content to b. reset src. */
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_move(buffer * restrict b, buffer * restrict src);
 
 /* make sure buffer is large enough to store a string of given size
@@ -51,7 +51,7 @@ void buffer_move(buffer * restrict b, buffer * restrict src);
  * sets b to an empty string, and may drop old content.
  * @return b->ptr
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 char* buffer_string_prepare_copy(buffer *b, size_t size);
 
@@ -61,7 +61,7 @@ char* buffer_string_prepare_copy(buffer *b, size_t size);
  * "used" data is preserved; if not empty buffer must contain a
  * zero terminated string.
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 char* buffer_string_prepare_append(buffer *b, size_t size);
 
@@ -69,7 +69,7 @@ char* buffer_string_prepare_append(buffer *b, size_t size);
  * buffer_string_prepare_append() which only ensures space is available)
  * returns pointer to which callers should immediately write x bytes
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 char* buffer_extend(buffer * const restrict b, size_t x);
 
@@ -78,7 +78,7 @@ char* buffer_extend(buffer * const restrict b, size_t x);
  * requires enough space is present for the terminating zero (prepare with the
  * same size to be sure).
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_commit(buffer *b, size_t size);
 
 /* clear buffer
@@ -86,7 +86,7 @@ void buffer_commit(buffer *b, size_t size);
  * - unsets used chars but does not modify existing ptr contents
  *   (b->ptr *is not* set to an empty, '\0'-terminated string "")
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_clear(buffer *b);
 
 /* reset buffer
@@ -96,14 +96,14 @@ static inline void buffer_clear(buffer *b);
  *   (b->ptr *is not* set to an empty, '\0'-terminated string "")
  * - frees larger buffer (b->size > BUFFER_MAX_REUSE_SIZE)
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_reset(buffer *b);
 
 /* free buffer ptr
  * - invalidate buffer contents; free ptr; reset ptr, used, size to 0
  */
 __attribute_cold__
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_free_ptr(buffer *b);
 
 void buffer_copy_string(buffer * restrict b, const char * restrict s);
@@ -123,13 +123,13 @@ struct const_iovec {
 };
 #endif
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_append_iovec(buffer * restrict b, const struct const_iovec *iov, size_t n);
 
 #define buffer_append_uint_hex(b,len) buffer_append_uint_hex_lc((b),(len))
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_append_uint_hex_lc(buffer *b, uintmax_t len);
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_append_int(buffer *b, intmax_t val);
 
 void buffer_append_strftime(buffer * restrict b, const char * restrict format, const struct tm * restrict tm);
@@ -137,44 +137,44 @@ void buffer_append_strftime(buffer * restrict b, const char * restrict format, c
 /* '-', log_10 (2^bits) = bits * log 2 / log 10 < bits * 0.31, terminating 0 */
 #define LI_ITOSTRING_LENGTH (2 + (8 * sizeof(intmax_t) * 31 + 99) / 100)
 
-__attribute_nonnull__
+__attribute_nonnull__()
 size_t li_itostrn(char *buf, size_t buf_len, intmax_t val);
-__attribute_nonnull__
+__attribute_nonnull__()
 size_t li_utostrn(char *buf, size_t buf_len, uintmax_t val);
 
 /* buf must be (at least) 2*s_len + 1 big. uses lower-case hex letters. */
 #define li_tohex(buf,buf_len,s,s_len) li_tohex_lc((buf),(buf_len),(s),(s_len))
-__attribute_nonnull__
+__attribute_nonnull__()
 void li_tohex_lc(char * restrict buf, size_t buf_len, const char * restrict s, size_t s_len);
-__attribute_nonnull__
+__attribute_nonnull__()
 void li_tohex_uc(char * restrict buf, size_t buf_len, const char * restrict s, size_t s_len);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int buffer_eq_icase_ssn(const char * const a, const char * const b, const size_t len);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int buffer_eq_icase_ss(const char * const a, const size_t alen, const char * const b, const size_t blen);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int buffer_eq_icase_slen(const buffer * const b, const char * const s, const size_t slen);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int buffer_eq_slen(const buffer * const b, const char * const s, const size_t slen);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int buffer_is_equal(const buffer *a, const buffer *b);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_substr_replace (buffer * restrict b, size_t offset, size_t len, const buffer * restrict replace);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_append_string_encoded_hex_lc(buffer * restrict b, const char * restrict s, size_t len);
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_append_string_encoded_hex_uc(buffer * restrict b, const char * restrict s, size_t len);
 
 typedef enum {
@@ -187,22 +187,22 @@ typedef enum {
 void buffer_append_string_encoded(buffer * restrict b, const char * restrict s, size_t s_len, buffer_encoding_t encoding);
 
 /* escape non-printable characters; simple escapes for \t, \r, \n; fallback to \xCC */
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_append_string_c_escaped(buffer * restrict b, const char * restrict s, size_t s_len);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_urldecode_path(buffer *b);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int buffer_is_valid_UTF8(const buffer *b);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_path_simplify(buffer *b);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_to_lower(buffer *b);
-__attribute_nonnull__
+__attribute_nonnull__()
 void buffer_to_upper(buffer *b);
 
 
@@ -248,11 +248,11 @@ static inline int light_isalnum(int c) {
 void buffer_append_path_len(buffer * restrict b, const char * restrict a, size_t alen); /* join strings with '/', if '/' not present */
 void buffer_copy_path_len2(buffer * restrict b, const char * restrict s1, size_t len1, const char * restrict s2, size_t len2);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 static inline int buffer_has_slash_suffix (const buffer * const b);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 static inline int buffer_has_pathsep_suffix (const buffer * const b);
 
@@ -265,14 +265,14 @@ static inline int buffer_has_pathsep_suffix (const buffer * const b);
 
 /* inline implementations */
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 static inline int buffer_is_unset(const buffer *b);
 static inline int buffer_is_unset(const buffer *b) {
     return 0 == b->used;
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 static inline int buffer_is_blank(const buffer *b);
 static inline int buffer_is_blank(const buffer *b) {
@@ -280,7 +280,7 @@ static inline int buffer_is_blank(const buffer *b) {
 }
 
 /* buffer "C" len (bytes) */
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 static inline uint32_t buffer_clen (const buffer *b);
 static inline uint32_t buffer_clen (const buffer *b) {
@@ -288,40 +288,40 @@ static inline uint32_t buffer_clen (const buffer *b) {
 }
 
 /* buffer space remaining to append string without reallocating */
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 static inline uint32_t buffer_string_space(const buffer *b);
 static inline uint32_t buffer_string_space(const buffer *b) {
     return b->size ? b->size - (b->used | (0 == b->used)) : 0;
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_copy_buffer(buffer * restrict b, const buffer * restrict src);
 static inline void buffer_copy_buffer(buffer * restrict b, const buffer * restrict src) {
     buffer_copy_string_len(b, BUF_PTR_LEN(src));
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_append_buffer(buffer * restrict b, const buffer * restrict src);
 static inline void buffer_append_buffer(buffer * restrict b, const buffer * restrict src) {
     buffer_append_string_len(b, BUF_PTR_LEN(src));
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_truncate(buffer *b, uint32_t len);
 static inline void buffer_truncate(buffer *b, uint32_t len) {
     b->ptr[len] = '\0'; /* b->ptr must exist; use buffer_blank() for trunc 0 */
     b->used = len + 1;
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_blank(buffer *b);
 static inline void buffer_blank(buffer *b) {
     b->ptr ? buffer_truncate(b, 0) : (void)buffer_extend(b, 0);
 }
 
 /* append '/' to non-empty strings not ending in '/' */
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_append_slash(buffer *b);
 static inline void buffer_append_slash(buffer *b) {
     const uint32_t len = buffer_clen(b);
@@ -391,7 +391,7 @@ static inline uint32_t buffer_string_length(const buffer *b) {
  * - does not modify the string data apart from terminating zero
  * - reallocates the buffer iff needed
  */
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void buffer_string_set_length(buffer *b, uint32_t len);
 static inline void buffer_string_set_length(buffer *b, uint32_t len) {
     if (len < b->size)
diff --git a/src/chunk.c b/src/chunk.c
index de38a8ab..b757cff7 100644
--- a/src/chunk.c
+++ b/src/chunk.c
@@ -371,7 +371,7 @@ static chunk * chunkqueue_append_mem_chunk(chunkqueue *cq, size_t sz) {
     return c;
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static chunk * chunkqueue_append_file_chunk(chunkqueue * const restrict cq, const buffer * const restrict fn, off_t offset, off_t len) {
     chunk * const c = chunk_acquire_filechunk();
diff --git a/src/chunk.h b/src/chunk.h
index 0d9b92e4..cfa11d52 100644
--- a/src/chunk.h
+++ b/src/chunk.h
@@ -60,7 +60,7 @@ buffer * chunk_buffer_acquire(void);
 
 void chunk_buffer_release(buffer *b);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void chunk_buffer_yield(buffer *b);
 
 size_t chunk_buffer_prepare_append (buffer *b, size_t sz);
@@ -87,10 +87,10 @@ void chunkqueue_append_file_fd(chunkqueue * restrict cq, const buffer * restrict
 void chunkqueue_append_mem(chunkqueue * restrict cq, const char * restrict mem, size_t len); /* copies memory */
 void chunkqueue_append_mem_min(chunkqueue * restrict cq, const char * restrict mem, size_t len); /* copies memory */
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void chunkqueue_append_buffer(chunkqueue * restrict cq, buffer * restrict mem); /* may reset "mem" */
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void chunkqueue_append_chunkqueue(chunkqueue * restrict cq, chunkqueue * restrict src);
 
 __attribute_returns_nonnull__
diff --git a/src/ck.c b/src/ck.c
index dc268e11..5a4c9d40 100644
--- a/src/ck.c
+++ b/src/ck.c
@@ -379,7 +379,7 @@ error:
 
 
 __attribute_noinline__
-__attribute_nonnull__
+__attribute_nonnull__()
 static void
 ck_bt_stderr (const char *filename, unsigned int line, const char *msg, const char *fmt)
 {
diff --git a/src/ck.h b/src/ck.h
index 4639ae89..c8ab4b4e 100644
--- a/src/ck.h
+++ b/src/ck.h
@@ -50,26 +50,26 @@ errno_t ck_strerror_s (char *s, rsize_t maxsize, errno_t errnum);
  * constant time memory compare for equality
  * rounds to next multiple of 64 to avoid potentially leaking exact
  * string lengths when subject to high precision timing attacks */
-__attribute_nonnull__
+__attribute_nonnull__()
 int ck_memeq_const_time (const void *a, size_t alen, const void *b, size_t blen);
 
 /*(ck_memeq_const_time_fixed_len() is not from C11 Annex K)
  * constant time memory compare for equality for fixed len (e.g. digests)
  * (padding not necessary for digests, which have fixed, defined lengths) */
-__attribute_nonnull__
+__attribute_nonnull__()
 int ck_memeq_const_time_fixed_len (const void *a, const void *b, size_t len);
 
 
 /*(ck_bt() is not from C11 Annex K)
  * ck_bt() prints backtrace to stderr */
 __attribute_cold__
-__attribute_nonnull__
+__attribute_nonnull__()
 void ck_bt(const char *filename, unsigned int line, const char *msg);
 
 /*(ck_bt_abort() is not from C11 Annex K)
  * ck_bt_abort() prints backtrace to stderr and calls abort() */
 __attribute_cold__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_noreturn__
 void ck_bt_abort(const char *filename, unsigned int line, const char *msg);
 
@@ -78,7 +78,7 @@ void ck_bt_abort(const char *filename, unsigned int line, const char *msg);
  * ck_assert() *is not* optimized away if defined(NDEBUG)
  * (unlike standard assert(), which *is* optimized away if defined(NDEBUG)) */
 __attribute_cold__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_noreturn__
 void ck_assert_failed(const char *filename, unsigned int line, const char *msg);
 
diff --git a/src/first.h b/src/first.h
index 9d0428ae..9f8380f4 100644
--- a/src/first.h
+++ b/src/first.h
@@ -246,9 +246,9 @@ typedef struct unix_timespec64 unix_timespec64_t;
 #ifndef __attribute_nonnull__
 #if __has_attribute(nonnull) \
  || __GNUC_PREREQ(3,3)
-#define __attribute_nonnull__  __attribute__((__nonnull__))
+#define __attribute_nonnull__(params)  __attribute__((__nonnull__ params))
 #else
-#define __attribute_nonnull__
+#define __attribute_nonnull__(params)
 #endif
 #endif
 
diff --git a/src/http_kv.h b/src/http_kv.h
index ce84f7ea..e793267b 100644
--- a/src/http_kv.h
+++ b/src/http_kv.h
@@ -71,7 +71,7 @@ const char *get_http_version_name(int i);
 #define get_http_method_name(i) http_method_buf(i)->ptr
 
 #if 0 /*(unused)*/
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 int get_http_version_key(const char *s, size_t slen);
 #endif
@@ -79,20 +79,20 @@ int get_http_version_key(const char *s, size_t slen);
 __attribute_pure__
 const buffer *http_method_buf (http_method_t i);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_pure__
 http_method_t get_http_method_key(const char *s, size_t slen);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void http_status_append(buffer *b, int status);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 void http_version_append(buffer *b, http_version_t version);
 
 #define http_method_get_or_head(method)   ((method) <= HTTP_METHOD_HEAD)
 #define http_method_get_head_post(method) ((method) <= HTTP_METHOD_POST)
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static inline void http_method_append (buffer * const b, const http_method_t method);
 static inline void http_method_append (buffer * const b, const http_method_t method) {
     const buffer * const kv = http_method_buf(method);
diff --git a/src/log.c b/src/log.c
index e0a8d15a..1835c476 100644
--- a/src/log.c
+++ b/src/log.c
@@ -95,7 +95,7 @@ ssize_t write_all(int fd, const void * const buf, size_t count) {
 }
 
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static void
 log_buffer_timestamp (buffer * const restrict b)
 {
@@ -136,7 +136,7 @@ log_buffer_timestamp (buffer * const restrict b)
 }
 
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static void
 log_buffer_prefix (buffer * const restrict b,
                    const char * const restrict filename,
@@ -168,7 +168,7 @@ log_buffer_append_encoded (buffer * const b,
 
 
 __attribute_format__((__printf__, 2, 0))
-__attribute_nonnull__
+__attribute_nonnull__()
 static void
 log_buffer_vsprintf (buffer * const restrict b,
                      const char * const restrict fmt, va_list ap)
@@ -207,7 +207,7 @@ log_buffer_vsprintf (buffer * const restrict b,
 }
 
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static buffer *
 log_buffer_prepare (const log_error_st * const errh,
                     const char * const restrict filename,
@@ -224,7 +224,7 @@ log_buffer_prepare (const log_error_st * const errh,
 }
 
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static void
 log_error_write (const log_error_st * const errh, buffer * const restrict b)
 {
diff --git a/src/mod_indexfile.c b/src/mod_indexfile.c
index a66fc3cf..e3235091 100644
--- a/src/mod_indexfile.c
+++ b/src/mod_indexfile.c
@@ -78,7 +78,7 @@ SETDEFAULTS_FUNC(mod_indexfile_set_defaults) {
     return HANDLER_GO_ON;
 }
 
-__attribute_nonnull__
+__attribute_nonnull__()
 static handler_t mod_indexfile_tryfiles(request_st * const r, const array * const indexfiles) {
 	for (uint32_t k = 0; k < indexfiles->used; ++k) {
 		const buffer * const v = &((data_string *)indexfiles->data[k])->value;
diff --git a/src/mod_magnet_cache.c b/src/mod_magnet_cache.c
index cf25350a..a476dd39 100644
--- a/src/mod_magnet_cache.c
+++ b/src/mod_magnet_cache.c
@@ -91,7 +91,7 @@ static lua_State *script_cache_load_script(script * const sc, int etag_flags)
 }
 
 __attribute_cold__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 static script *script_cache_new_script(script_cache * const cache, const buffer * const name)
 {
diff --git a/src/mod_magnet_cache.h b/src/mod_magnet_cache.h
index 3dc6d04a..49df0586 100644
--- a/src/mod_magnet_cache.h
+++ b/src/mod_magnet_cache.h
@@ -31,11 +31,11 @@ __attribute_cold__
 void script_cache_free_data(script_cache *cache);
 
 __attribute_cold__
-__attribute_nonnull__
+__attribute_nonnull__()
 __attribute_returns_nonnull__
 script *script_cache_get_script(script_cache *cache, const buffer *name);
 
-__attribute_nonnull__
+__attribute_nonnull__()
 lua_State *script_cache_check_script(script * const sc, int etag_flags);
 
 #endif
diff --git a/src/server.c b/src/server.c
index 3eed0aa0..682fef49 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1910,7 +1910,7 @@ static void server_handle_sigchld (server * const srv) {
 }
 
 __attribute_hot__
-__attribute_nonnull__
+__attribute_nonnull__()
 static void server_run_con_queue (connection * const restrict joblist, const connection * const sentinel) {
     for (connection *con = joblist, *jqnext; con != sentinel; con = jqnext) {
         jqnext = con->jqnext;