diff --git a/main.c b/main.c
index 56094cc..77a98ba 100644
--- a/main.c
+++ b/main.c
@@ -180,12 +180,19 @@ char *make_full_path (char *s) {
   return s;
 }
 
-void running_for_first_time (void) {
-  if (sizeof (void) != 1) {
-    logprintf ("sizeof (void) isn't equal 1\n");
-    logprintf ("GNU C compiler extension isn't available?\n");
+void check_type_sizes (void) {
+  if (sizeof (int) != 4u) {
+    logprintf ("sizeof (int) isn't equal 4.\n");
     exit (1);
   }
+  if (sizeof (char) != 1u) {
+    logprintf ("sizeof (char) isn't equal 1.\n");
+    exit (1);
+  }
+}
+
+void running_for_first_time (void) {
+  check_type_sizes ();
   if (config_filename) {
     return; // Do not create custom config file
   }
diff --git a/mtproto-common.c b/mtproto-common.c
index 2d87f83..4ef429f 100644
--- a/mtproto-common.c
+++ b/mtproto-common.c
@@ -52,7 +52,7 @@ long long rsa_encrypted_chunks, rsa_decrypted_chunks;
 BN_CTX *BN_ctx;
 int verbosity;
 
-int get_random_bytes (void *buf, int n) {
+int get_random_bytes (unsigned char *buf, int n) {
   int r = 0, h = open ("/dev/random", O_RDONLY | O_NONBLOCK);
   if (h >= 0) {
     r = read (h, buf, n);
diff --git a/mtproto-common.h b/mtproto-common.h
index 0b8bffd..7cd6691 100644
--- a/mtproto-common.h
+++ b/mtproto-common.h
@@ -427,7 +427,7 @@ static inline void fetch_ints (void *data, int count) {
   in_ptr += count;
 }
 
-int get_random_bytes (void *buf, int n);
+int get_random_bytes (unsigned char *buf, int n);
 
 int pad_rsa_encrypt (char *from, int from_len, char *to, int size, BIGNUM *N, BIGNUM *E);
 int pad_rsa_decrypt (char *from, int from_len, char *to, int size, BIGNUM *N, BIGNUM *D);
diff --git a/net.c b/net.c
index 3ecfa51..ccd5db9 100644
--- a/net.c
+++ b/net.c
@@ -115,7 +115,8 @@ void delete_connection_buffer (struct connection_buffer *b) {
   free (b);
 }
 
-int write_out (struct connection *c, const void *data, int len) {
+int write_out (struct connection *c, const void *_data, int len) {
+  const unsigned char *data = _data;
   if (!len) { return 0; }
   assert (len > 0);
   int x = 0;
@@ -146,7 +147,8 @@ int write_out (struct connection *c, const void *data, int len) {
   return x;
 }
 
-int read_in (struct connection *c, void *data, int len) {
+int read_in (struct connection *c, void *_data, int len) {
+  unsigned char *data = _data;
   if (!len) { return 0; }
   assert (len > 0);
   if (len > c->in_bytes) {
@@ -177,7 +179,8 @@ int read_in (struct connection *c, void *data, int len) {
   return x;
 }
 
-int read_in_lookup (struct connection *c, void *data, int len) {
+int read_in_lookup (struct connection *c, void *_data, int len) {
+  unsigned char *data = _data;
   if (!len || !c->in_bytes) { return 0; }
   assert (len > 0);
   if (len > c->in_bytes) {
diff --git a/net.h b/net.h
index 69a473b..181c46c 100644
--- a/net.h
+++ b/net.h
@@ -93,10 +93,10 @@ struct dc_serialized {
 };
 
 struct connection_buffer {
-  void *start;
-  void *end;
-  void *rptr;
-  void *wptr;
+  unsigned char *start;
+  unsigned char *end;
+  unsigned char *rptr;
+  unsigned char *wptr;
   struct connection_buffer *next;
 };
 
diff --git a/queries.c b/queries.c
index 7eaff00..aa3321b 100644
--- a/queries.c
+++ b/queries.c
@@ -2329,7 +2329,7 @@ void do_create_keys_end (struct secret_chat *U) {
   ensure_ptr (a);
   ensure (BN_mod_exp (r, g_b, a, p, ctx));
 
-  void *t = talloc (256);
+  unsigned char *t = talloc (256);
   memcpy (t, U->key, 256);
   
   memset (U->key, 0, sizeof (U->key));