diff --git a/src/common/aes.h b/src/common/aes.h
index 3c63a0e4f2..085ea55932 100644
--- a/src/common/aes.h
+++ b/src/common/aes.h
@@ -17,7 +17,7 @@
 struct aes_cnt_cipher;
 typedef struct aes_cnt_cipher aes_cnt_cipher_t;
 
-aes_cnt_cipher_t* aes_new_cipher();
+aes_cnt_cipher_t* aes_new_cipher(void);
 void aes_free_cipher(aes_cnt_cipher_t *cipher);
 void aes_set_key(aes_cnt_cipher_t *cipher, const unsigned char *key, int key_bits);
 void aes_crypt(aes_cnt_cipher_t *cipher, const char *input, int len, char *output);
diff --git a/src/common/crypto.c b/src/common/crypto.c
index 0ab6d3d3c4..b4659078bc 100644
--- a/src/common/crypto.c
+++ b/src/common/crypto.c
@@ -1175,7 +1175,7 @@ static BIGNUM *dh_param_g = NULL;
 
 /** Initialize dh_param_p and dh_param_g if they are not already
  * set. */
-static void init_dh_param() {
+static void init_dh_param(void) {
   BIGNUM *p, *g;
   int r;
   if (dh_param_p && dh_param_g)
@@ -1366,7 +1366,7 @@ void crypto_dh_free(crypto_dh_env_t *dh)
 /** Seed OpenSSL's random number generator with DIGEST_LEN bytes from the
  * operating system.  Return 0 on suuccess, -1 on failure.
  */
-int crypto_seed_rng()
+int crypto_seed_rng(void)
 {
 #ifdef MS_WINDOWS
   static int provider_set = 0;
diff --git a/src/common/crypto.h b/src/common/crypto.h
index 33e4006c1c..c6df8f0021 100644
--- a/src/common/crypto.h
+++ b/src/common/crypto.h
@@ -46,8 +46,8 @@ typedef struct crypto_digest_env_t crypto_digest_env_t;
 typedef struct crypto_dh_env_t crypto_dh_env_t;
 
 /* global state */
-int crypto_global_init();
-int crypto_global_cleanup();
+int crypto_global_init(void);
+int crypto_global_cleanup(void);
 
 /* environment setup */
 crypto_pk_env_t *crypto_new_pk_env(void);
@@ -100,7 +100,7 @@ void base16_encode(char *dest, size_t destlen, const char *src, size_t srclen);
 int base16_decode(char *dest, size_t destlen, const char *src, size_t srclen);
 
 /* Key negotiation */
-crypto_dh_env_t *crypto_dh_new();
+crypto_dh_env_t *crypto_dh_new(void);
 int crypto_dh_get_bytes(crypto_dh_env_t *dh);
 int crypto_dh_generate_public(crypto_dh_env_t *dh);
 int crypto_dh_get_public(crypto_dh_env_t *dh, char *pubkey_out,
@@ -129,7 +129,7 @@ crypto_cipher_env_t *crypto_create_init_cipher(const char *key, int encrypt_mode
 
 /* SHA-1 */
 int crypto_digest(const unsigned char *m, int len, unsigned char *digest);
-crypto_digest_env_t *crypto_new_digest_env();
+crypto_digest_env_t *crypto_new_digest_env(void);
 void crypto_free_digest_env(crypto_digest_env_t *digest);
 void crypto_digest_add_bytes(crypto_digest_env_t *digest, const char *data,
                              size_t len);
@@ -140,7 +140,7 @@ void crypto_digest_assign(crypto_digest_env_t *into,
                           const crypto_digest_env_t *from);
 
 /* random numbers */
-int crypto_seed_rng();
+int crypto_seed_rng(void);
 int crypto_rand(unsigned int n, unsigned char *to);
 void crypto_pseudo_rand(unsigned int n, unsigned char *to);
 int crypto_pseudo_rand_int(unsigned int max);
diff --git a/src/common/tortls.c b/src/common/tortls.c
index 03b55c0191..eaef6468bf 100644
--- a/src/common/tortls.c
+++ b/src/common/tortls.c
@@ -147,7 +147,7 @@ tor_tls_get_error(tor_tls *tls, int r, int extra,
 /** Initialize OpenSSL, unless it has already been initialized.
  */
 static void
-tor_tls_init() {
+tor_tls_init(void) {
   if (!tls_library_is_initialized) {
     SSL_library_init();
     SSL_load_error_strings();
diff --git a/src/common/util.h b/src/common/util.h
index f9f50f086e..0b6ffd77e3 100644
--- a/src/common/util.h
+++ b/src/common/util.h
@@ -140,7 +140,7 @@ const char *hex_str(const char *from, size_t fromlen);
 /** Generic resizeable array. */
 typedef struct smartlist_t smartlist_t;
 
-smartlist_t *smartlist_create();
+smartlist_t *smartlist_create(void);
 void smartlist_free(smartlist_t *sl);
 void smartlist_set_capacity(smartlist_t *sl, int n);
 void smartlist_clear(smartlist_t *sl);
@@ -234,7 +234,7 @@ char *expand_filename(const char *filename);
 int replace_file(const char *from, const char *to);
 
 int spawn_func(int (*func)(void *), void *data);
-void spawn_exit();
+void spawn_exit(void);
 
 /* Because we use threads instead of processes on Windows, we need locking on Windows.
  * On Unixy platforms, these functions are no-ops. */
diff --git a/src/or/or.h b/src/or/or.h
index 780cff32fc..92bf66e97b 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -948,7 +948,7 @@ struct socks_request_t {
 
 /********************************* buffers.c ***************************/
 
-buf_t *buf_new();
+buf_t *buf_new(void);
 buf_t *buf_new_with_capacity(size_t size);
 void buf_free(buf_t *buf);
 void buf_clear(buf_t *buf);
@@ -1207,11 +1207,11 @@ int connection_dir_finished_connecting(connection_t *conn);
 int dirserv_add_own_fingerprint(const char *nickname, crypto_pk_env_t *pk);
 int dirserv_parse_fingerprint_file(const char *fname);
 int dirserv_router_fingerprint_is_known(const routerinfo_t *router);
-void dirserv_free_fingerprint_list();
+void dirserv_free_fingerprint_list(void);
 const char *dirserv_get_nickname_by_digest(const char *digest);
 int dirserv_add_descriptor(const char **desc);
 int dirserv_load_from_directory_string(const char *dir);
-void dirserv_free_descriptors();
+void dirserv_free_descriptors(void);
 void dirserv_remove_old_servers(int age);
 int dirserv_dump_directory_to_string(char *s, size_t maxlen,
                                      crypto_pk_env_t *private_key);
diff --git a/src/or/test.c b/src/or/test.c
index 0ce384ad5b..45521b4fcd 100644
--- a/src/or/test.c
+++ b/src/or/test.c
@@ -44,7 +44,7 @@ dump_hex(char *s, size_t len)
 static char temp_dir[256];
 
 void
-setup_directory()
+setup_directory(void)
 {
   static int is_setup = 0;
   int r;
@@ -74,7 +74,7 @@ get_fname(const char *name)
 }
 
 void
-remove_directory()
+remove_directory(void)
 {
   DIR *dirp;
   struct dirent *de;
@@ -98,7 +98,7 @@ remove_directory()
 }
 
 void
-test_buffers() {
+test_buffers(void) {
 #define MAX_BUF_SIZE 1024*1024
   char str[256];
   char str2[256];
@@ -224,7 +224,7 @@ test_buffers() {
 }
 
 void
-test_crypto_dh()
+test_crypto_dh(void)
 {
   crypto_dh_env_t *dh1, *dh2;
   char p1[DH_BYTES];
@@ -259,7 +259,7 @@ test_crypto_dh()
 }
 
 void
-test_crypto()
+test_crypto(void)
 {
   crypto_cipher_env_t *env1, *env2;
   crypto_pk_env_t *pk1, *pk2;
@@ -495,7 +495,7 @@ test_crypto()
 }
 
 void
-test_util() {
+test_util(void) {
   struct timeval start, end;
   struct tm a_time;
   smartlist_t *sl;
@@ -695,7 +695,8 @@ test_util() {
 }
 
 void
-test_gzip() {
+test_gzip(void)
+{
   char *buf1, *buf2=NULL, *buf3=NULL;
   size_t len1, len2;
 
@@ -740,7 +741,8 @@ static void* _squareAndRemoveK4(const char *key, void*val, void *data)
   return (void*)(v*v);
 }
 
-void test_strmap() {
+void test_strmap(void)
+{
   strmap_t *map;
   strmap_iter_t *iter;
   const char *k;
@@ -813,7 +815,8 @@ void test_strmap() {
   strmap_free(map,NULL);
 }
 
-void test_onion() {
+void test_onion(void)
+{
 #if 0
   char **names;
   int i,num;
@@ -831,7 +834,8 @@ void test_onion() {
 }
 
 void
-test_onion_handshake() {
+test_onion_handshake(void)
+{
   /* client-side */
   crypto_dh_env_t *c_dh = NULL;
   char c_buf[ONIONSKIN_CHALLENGE_LEN];
@@ -876,7 +880,7 @@ test_onion_handshake() {
 int is_obsolete_version(const char *myversion, const char *start);
 
 void
-test_dir_format()
+test_dir_format(void)
 {
   char buf[8192], buf2[8192];
   char platform[256];
@@ -1124,7 +1128,7 @@ test_dir_format()
 
 }
 
-void test_rend_fns()
+void test_rend_fns(void)
 {
   char address1[] = "fooaddress.onion";
   char address2[] = "aaaaaaaaaaaaaaaa.onion";