diff --git a/include/mysql_com.h b/include/mysql_com.h
index 14e8574c623..969e5364ce7 100644
--- a/include/mysql_com.h
+++ b/include/mysql_com.h
@@ -717,7 +717,7 @@ void scramble(char *to, const char *message, const char *password);
 my_bool check_scramble(const unsigned char *reply, const char *message,
                        const unsigned char *hash_stage2);
 void get_salt_from_password(unsigned char *res, const char *password);
-char *octet2hex(char *to, const char *str, size_t len);
+char *octet2hex(char *to, const unsigned char *str, size_t len);
 
 /* end of password.c */
 
diff --git a/sql/item.cc b/sql/item.cc
index a385cb67f30..a1a5e5f3c28 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -6547,7 +6547,7 @@ String *Item::check_well_formed_result(String *str, bool send_error)
     char hexbuf[7];
     uint diff= str->length() - wlen;
     set_if_smaller(diff, 3);
-    octet2hex(hexbuf, str->ptr() + wlen, diff);
+    octet2hex(hexbuf, (uchar*)str->ptr() + wlen, diff);
     if (send_error)
     {
       my_error(ER_INVALID_CHARACTER_STRING, MYF(0),
@@ -6599,7 +6599,7 @@ String_copier_for_item::copy_with_warn(CHARSET_INFO *dstcs, String *dst,
     char buf[16];
     int mblen= srccs->charlen(pos, src + src_length);
     DBUG_ASSERT(mblen > 0 && mblen * 2 + 1 <= (int) sizeof(buf));
-    octet2hex(buf, pos, mblen);
+    octet2hex(buf, (uchar*)pos, mblen);
     push_warning_printf(m_thd, Sql_condition::WARN_LEVEL_WARN,
                         ER_CANNOT_CONVERT_CHARACTER,
                         ER_THD(m_thd, ER_CANNOT_CONVERT_CHARACTER),
diff --git a/sql/log_event.cc b/sql/log_event.cc
index f167284ad1d..df791c483ef 100644
--- a/sql/log_event.cc
+++ b/sql/log_event.cc
@@ -259,7 +259,7 @@ static inline bool read_str(const uchar **buf, const uchar *buf_end,
   Transforms a string into "" or its expression in X'HHHH' form.
 */
 
-char *str_to_hex(char *to, const char *from, size_t len)
+char *str_to_hex(char *to, const uchar *from, size_t len)
 {
   if (len)
   {
diff --git a/sql/log_event.h b/sql/log_event.h
index d324642ad5e..1672e8f140d 100644
--- a/sql/log_event.h
+++ b/sql/log_event.h
@@ -3746,7 +3746,7 @@ public:
   bool is_valid() const { return 1; }
 };
 #endif
-char *str_to_hex(char *to, const char *from, size_t len);
+char *str_to_hex(char *to, const uchar *from, size_t len);
 
 /**
   @class Annotate_rows_log_event
diff --git a/sql/log_event_client.cc b/sql/log_event_client.cc
index be680408d55..5080b8bc5ad 100644
--- a/sql/log_event_client.cc
+++ b/sql/log_event_client.cc
@@ -1541,7 +1541,7 @@ bool Rows_log_event::print_verbose(IO_CACHE *file,
       */
       const int buff_len= 2 + (256 * 2) + 1;
       char buff[buff_len];
-      str_to_hex(buff, (const char*) &m_extra_row_data[EXTRA_ROW_INFO_HDR_BYTES],
+      str_to_hex(buff, &m_extra_row_data[EXTRA_ROW_INFO_HDR_BYTES],
                  extra_payload_len);
       if (my_b_printf(file, "%s", buff))
         goto err;
@@ -2540,7 +2540,7 @@ bool User_var_log_event::print(FILE* file, PRINT_EVENT_INFO* print_event_info)
       hex_str= (char *) my_malloc(PSI_NOT_INSTRUMENTED, 2 * val_len + 1 + 3, MYF(MY_WME));
       if (!hex_str)
         goto err;
-      str_to_hex(hex_str, val, val_len);
+      str_to_hex(hex_str, (uchar*)val, val_len);
       /*
         For proper behaviour when mysqlbinlog|mysql, we need to explicitly
         specify the variable's collation. It will however cause problems when
diff --git a/sql/log_event_server.cc b/sql/log_event_server.cc
index 2add655defc..ae2eb319d56 100644
--- a/sql/log_event_server.cc
+++ b/sql/log_event_server.cc
@@ -503,7 +503,7 @@ int append_query_string(CHARSET_INFO *csinfo, String *to,
   beg= (char*) to->ptr() + to->length();
   ptr= beg;
   if (csinfo->escape_with_backslash_is_dangerous)
-    ptr= str_to_hex(ptr, str, len);
+    ptr= str_to_hex(ptr, (uchar*)str, len);
   else
   {
     *ptr++= '\'';
@@ -3885,7 +3885,7 @@ void User_var_log_event::pack_info(Protocol* protocol)
                         MY_CS_COLLATION_NAME_SIZE))
           return;
         beg= const_cast<char *>(buf.ptr()) + old_len;
-        end= str_to_hex(beg, val, val_len);
+        end= str_to_hex(beg, (uchar*)val, val_len);
         buf.length(old_len + (end - beg));
         if (buf.append(STRING_WITH_LEN(" COLLATE ")) ||
             buf.append(cs->coll_name))
diff --git a/sql/password.c b/sql/password.c
index d824e61586a..6ad5cd16202 100644
--- a/sql/password.c
+++ b/sql/password.c
@@ -296,13 +296,13 @@ void make_password_from_salt_323(char *to, const ulong *salt)
     buf+len*2
 */
 
-char *octet2hex(char *to, const char *str, size_t len)
+char *octet2hex(char *to, const uchar *str, size_t len)
 {
-  const char *str_end= str + len; 
+  const uchar *str_end= str + len;
   for (; str != str_end; ++str)
   {
-    *to++= _dig_vec_upper[((uchar) *str) >> 4];
-    *to++= _dig_vec_upper[((uchar) *str) & 0x0F];
+    *to++= _dig_vec_upper[*str >> 4];
+    *to++= _dig_vec_upper[*str & 0x0F];
   }
   *to= '\0';
   return to;
@@ -399,7 +399,7 @@ void my_make_scrambled_password(char *to, const char *password,
 
   /* convert hash_stage2 to hex string */
   *to++= PVERSION41_CHAR;
-  octet2hex(to, (const char*) hash_stage2, MY_SHA1_HASH_SIZE);
+  octet2hex(to, hash_stage2, MY_SHA1_HASH_SIZE);
 }
   
 
@@ -519,6 +519,6 @@ void get_salt_from_password(uint8 *hash_stage2, const char *password)
 void make_password_from_salt(char *to, const uint8 *hash_stage2)
 {
   *to++= PVERSION41_CHAR;
-  octet2hex(to, (const char*) hash_stage2, MY_SHA1_HASH_SIZE);
+  octet2hex(to, hash_stage2, MY_SHA1_HASH_SIZE);
 }
 
diff --git a/sql/semisync_master.cc b/sql/semisync_master.cc
index 670a6d8d9ed..24ff7b9e8fe 100644
--- a/sql/semisync_master.cc
+++ b/sql/semisync_master.cc
@@ -603,7 +603,7 @@ l_end:
   if (result == -1)
   {
     char buf[256];
-    octet2hex(buf, (const char*) packet, std::min(static_cast<ulong>(sizeof(buf)-1),
+    octet2hex(buf, packet, std::min(static_cast<ulong>(sizeof(buf)-1),
                                                   packet_len));
     sql_print_information("First bytes of the packet from semisync slave "
                           "server-id %d: %s", server_id, buf);
diff --git a/sql/unireg.cc b/sql/unireg.cc
index d936e047801..6cc4bc8495c 100644
--- a/sql/unireg.cc
+++ b/sql/unireg.cc
@@ -922,7 +922,7 @@ static bool pack_header(THD *thd, uchar *forminfo,
           hex_length= length * 2;
           tmpint->type_lengths[pos]= (uint) hex_length;
           tmpint->type_names[pos]= dst= (char*) thd->alloc(hex_length + 1);
-          octet2hex(dst, src, length);
+          octet2hex(dst, (uchar*)src, length);
         }
       }
 
diff --git a/storage/federated/ha_federated.cc b/storage/federated/ha_federated.cc
index efb598bf91e..db310b15955 100644
--- a/storage/federated/ha_federated.cc
+++ b/storage/federated/ha_federated.cc
@@ -1008,7 +1008,7 @@ static bool emit_key_part_element(String *to, KEY_PART_INFO *part,
 
     *buf++= '0';
     *buf++= 'x';
-    buf= octet2hex(buf, (char*) ptr, len);
+    buf= octet2hex(buf, ptr, len);
     if (to->append((char*) buff, (uint)(buf - buff)))
       DBUG_RETURN(1);
   }
diff --git a/storage/federatedx/ha_federatedx.cc b/storage/federatedx/ha_federatedx.cc
index 9a8a2a9044d..3a62d33278a 100644
--- a/storage/federatedx/ha_federatedx.cc
+++ b/storage/federatedx/ha_federatedx.cc
@@ -952,7 +952,7 @@ static bool emit_key_part_element(String *to, KEY_PART_INFO *part,
 
     *buf++= '0';
     *buf++= 'x';
-    buf= octet2hex(buf, (char*) ptr, len);
+    buf= octet2hex(buf, ptr, len);
     if (to->append((char*) buff, (uint)(buf - buff)))
       DBUG_RETURN(1);
   }