diff --git a/mysql-test/include/ctype_common.inc b/mysql-test/include/ctype_common.inc
index 202c508a9c9..9ee0a40c8ce 100644
--- a/mysql-test/include/ctype_common.inc
+++ b/mysql-test/include/ctype_common.inc
@@ -51,6 +51,15 @@ SELECT c1 as want1result  from t1 where c1 like 'locatio%';
 SELECT c1 as want1result  from t1 where c1 like 'location%';
 DROP TABLE t1;
 
+#
+# Bug #31070: crash during conversion of charsets
+#
+create table t1 (a set('a') not null);
+insert into t1 values (),();
+select cast(a as char(1)) from t1;
+select a sounds like a from t1;
+drop table t1;
+
 DROP DATABASE d1;
 # Restore settings
 USE test;
diff --git a/mysql-test/r/ctype_big5.result b/mysql-test/r/ctype_big5.result
index 6d318a445f5..b190273cc64 100644
--- a/mysql-test/r/ctype_big5.result
+++ b/mysql-test/r/ctype_big5.result
@@ -52,6 +52,19 @@ SELECT c1 as want1result  from t1 where c1 like 'location%';
 want1result
 location
 DROP TABLE t1;
+create table t1 (a set('a') not null);
+insert into t1 values (),();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+select cast(a as char(1)) from t1;
+cast(a as char(1))
+
+
+select a sounds like a from t1;
+a sounds like a
+1
+1
+drop table t1;
 DROP DATABASE d1;
 USE test;
 SET character_set_server= @safe_character_set_server;
diff --git a/mysql-test/r/ctype_euckr.result b/mysql-test/r/ctype_euckr.result
index 6017bc07763..b9619370d4c 100644
--- a/mysql-test/r/ctype_euckr.result
+++ b/mysql-test/r/ctype_euckr.result
@@ -52,6 +52,19 @@ SELECT c1 as want1result  from t1 where c1 like 'location%';
 want1result
 location
 DROP TABLE t1;
+create table t1 (a set('a') not null);
+insert into t1 values (),();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+select cast(a as char(1)) from t1;
+cast(a as char(1))
+
+
+select a sounds like a from t1;
+a sounds like a
+1
+1
+drop table t1;
 DROP DATABASE d1;
 USE test;
 SET character_set_server= @safe_character_set_server;
diff --git a/mysql-test/r/ctype_gb2312.result b/mysql-test/r/ctype_gb2312.result
index 314c336bab9..90c94c3b299 100644
--- a/mysql-test/r/ctype_gb2312.result
+++ b/mysql-test/r/ctype_gb2312.result
@@ -52,6 +52,19 @@ SELECT c1 as want1result  from t1 where c1 like 'location%';
 want1result
 location
 DROP TABLE t1;
+create table t1 (a set('a') not null);
+insert into t1 values (),();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+select cast(a as char(1)) from t1;
+cast(a as char(1))
+
+
+select a sounds like a from t1;
+a sounds like a
+1
+1
+drop table t1;
 DROP DATABASE d1;
 USE test;
 SET character_set_server= @safe_character_set_server;
diff --git a/mysql-test/r/ctype_gbk.result b/mysql-test/r/ctype_gbk.result
index 3f5d8b0d8c6..fe90c7bff29 100644
--- a/mysql-test/r/ctype_gbk.result
+++ b/mysql-test/r/ctype_gbk.result
@@ -52,6 +52,19 @@ SELECT c1 as want1result  from t1 where c1 like 'location%';
 want1result
 location
 DROP TABLE t1;
+create table t1 (a set('a') not null);
+insert into t1 values (),();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+select cast(a as char(1)) from t1;
+cast(a as char(1))
+
+
+select a sounds like a from t1;
+a sounds like a
+1
+1
+drop table t1;
 DROP DATABASE d1;
 USE test;
 SET character_set_server= @safe_character_set_server;
diff --git a/mysql-test/r/ctype_uca.result b/mysql-test/r/ctype_uca.result
index 889702e380c..e676d5a5ca0 100644
--- a/mysql-test/r/ctype_uca.result
+++ b/mysql-test/r/ctype_uca.result
@@ -2587,6 +2587,19 @@ SELECT c1 as want1result  from t1 where c1 like 'location%';
 want1result
 location
 DROP TABLE t1;
+create table t1 (a set('a') not null);
+insert into t1 values (),();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+select cast(a as char(1)) from t1;
+cast(a as char(1))
+
+
+select a sounds like a from t1;
+a sounds like a
+1
+1
+drop table t1;
 DROP DATABASE d1;
 USE test;
 SET character_set_server= @safe_character_set_server;
diff --git a/mysql-test/r/variables.result b/mysql-test/r/variables.result
index 19b48efe6b4..638d71c6940 100644
--- a/mysql-test/r/variables.result
+++ b/mysql-test/r/variables.result
@@ -286,6 +286,8 @@ select * from information_schema.session_variables where variable_name like 'net
 VARIABLE_NAME	VARIABLE_VALUE
 NET_BUFFER_LENGTH	1024
 set net_buffer_length=2000000000;
+Warnings:
+Warning	1292	Truncated incorrect net_buffer_length value: '2000000000'
 show variables like 'net_buffer_length';
 Variable_name	Value
 net_buffer_length	1048576
diff --git a/mysql-test/t/variables.test b/mysql-test/t/variables.test
index 81db143b518..f474d166fae 100644
--- a/mysql-test/t/variables.test
+++ b/mysql-test/t/variables.test
@@ -161,6 +161,7 @@ select * from information_schema.session_variables where variable_name like 'net
 set net_buffer_length=1;
 show variables like 'net_buffer_length';
 select * from information_schema.session_variables where variable_name like 'net_buffer_length';
+--warning 1292
 set net_buffer_length=2000000000;
 show variables like 'net_buffer_length';
 select * from information_schema.session_variables where variable_name like 'net_buffer_length';
diff --git a/mysys/my_getopt.c b/mysys/my_getopt.c
index 3a5b130e067..5b5c0881314 100644
--- a/mysys/my_getopt.c
+++ b/mysys/my_getopt.c
@@ -19,6 +19,7 @@
 #include <my_sys.h>
 #include <mysys_err.h>
 #include <my_getopt.h>
+#include <errno.h>
 
 static void default_reporter(enum loglevel level, const char *format, ...);
 my_error_reporter my_getopt_error_reporter= &default_reporter;
@@ -730,7 +731,15 @@ static longlong eval_num_suffix(char *argument, int *error, char *option_name)
   longlong num;
   
   *error= 0;
+  errno= 0;
   num= strtoll(argument, &endchar, 10);
+  if (errno == ERANGE)
+  {
+    my_getopt_error_reporter(ERROR_LEVEL,
+                             "Incorrect integer value: '%s'", argument);
+    *error= 1;
+    return 0;
+  }
   if (*endchar == 'k' || *endchar == 'K')
     num*= 1024L;
   else if (*endchar == 'm' || *endchar == 'M')
@@ -767,7 +776,14 @@ static longlong getopt_ll(char *arg, const struct my_option *optp, int *err)
   num= eval_num_suffix(arg, err, (char*) optp->name);
   if (num > 0 && (ulonglong) num > (ulonglong) optp->max_value &&
       optp->max_value) /* if max value is not set -> no upper limit */
+  {
+    char buf[22];
+    my_getopt_error_reporter(WARNING_LEVEL,
+                             "Truncated incorrect %s value: '%s'", 
+                             optp->name, llstr(num, buf));
+    
     num= (ulonglong) optp->max_value;
+  }
   num= ((num - optp->sub_size) / block_size);
   num= (longlong) (num * block_size);
   return max(num, optp->min_value);
diff --git a/sql/set_var.cc b/sql/set_var.cc
index 697de9cda97..ec82b56d793 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -1188,16 +1188,31 @@ bool sys_var_thd_ulong::check(THD *thd, set_var *var)
 bool sys_var_thd_ulong::update(THD *thd, set_var *var)
 {
   ulonglong tmp= var->save_result.ulonglong_value;
+  char buf[22];
+  bool truncated= false;
 
   /* Don't use bigger value than given with --maximum-variable-name=.. */
   if ((ulong) tmp > max_system_variables.*offset)
+  {
+    truncated= true;
+    llstr(tmp, buf);
     tmp= max_system_variables.*offset;
+  }
 
 #if SIZEOF_LONG == 4
   /* Avoid overflows on 32 bit systems */
   if (tmp > (ulonglong) ~(ulong) 0)
+  {
+    truncated= true;
+    llstr(tmp, buf);
     tmp= ((ulonglong) ~(ulong) 0);
+  }
 #endif
+  if (truncated)
+    push_warning_printf(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
+                        ER_TRUNCATED_WRONG_VALUE,
+                        ER(ER_TRUNCATED_WRONG_VALUE), name,
+                        buf);
 
   if (option_limits)
     tmp= (ulong) getopt_ull_limit_value(tmp, option_limits);
diff --git a/strings/ctype-big5.c b/strings/ctype-big5.c
index 7bb811a3064..ecfd3d648e0 100644
--- a/strings/ctype-big5.c
+++ b/strings/ctype-big5.c
@@ -6272,12 +6272,12 @@ my_mb_wc_big5(CHARSET_INFO *cs __attribute__((unused)),
 	      my_wc_t *pwc,const uchar *s,const uchar *e)
 {
 
-  int hi=s[0];
+  int hi;
   
   if (s >= e)
     return MY_CS_TOOSMALL;
   
-  if (hi<0x80)
+  if ((hi= s[0]) < 0x80)
   {
     pwc[0]=hi;
     return 1;
diff --git a/strings/ctype-euc_kr.c b/strings/ctype-euc_kr.c
index 844d8cc3ff5..fd783015bf4 100644
--- a/strings/ctype-euc_kr.c
+++ b/strings/ctype-euc_kr.c
@@ -8614,12 +8614,12 @@ my_mb_wc_euc_kr(CHARSET_INFO *cs __attribute__((unused)),
 		 my_wc_t *pwc, const uchar *s, const uchar *e)
 {
   
-  int hi=s[0];
+  int hi;
   
   if (s >= e)
     return MY_CS_TOOSMALL;
   
-  if (hi<0x80)
+  if ((hi= s[0]) < 0x80)
   {
     pwc[0]=hi;
     return 1;
diff --git a/strings/ctype-gb2312.c b/strings/ctype-gb2312.c
index 21aeb8b7990..4b3518ce3d2 100644
--- a/strings/ctype-gb2312.c
+++ b/strings/ctype-gb2312.c
@@ -5664,12 +5664,10 @@ my_mb_wc_gb2312(CHARSET_INFO *cs  __attribute__((unused)),
 		my_wc_t *pwc, const uchar *s, const uchar *e){
   int hi;
   
-  hi=(int) s[0];
-  
   if (s >= e)
     return MY_CS_TOOSMALL;
   
-  if (hi<0x80)
+  if ((hi= s[0]) < 0x80)
   {
     pwc[0]=hi;
     return 1;
diff --git a/strings/ctype-sjis.c b/strings/ctype-sjis.c
index ace457af63c..3925b76869c 100644
--- a/strings/ctype-sjis.c
+++ b/strings/ctype-sjis.c
@@ -4527,12 +4527,12 @@ mb:
 static int 
 my_mb_wc_sjis(CHARSET_INFO *cs  __attribute__((unused)),
 	      my_wc_t *pwc, const uchar *s, const uchar *e){
-  int hi=s[0];
+  int hi;
   
   if (s >= e)
     return MY_CS_TOOSMALL;
   
-  if (hi < 0x80)
+  if ((hi= s[0]) < 0x80)
   {
     pwc[0]=hi;
     return 1;