diff --git a/mysql-test/r/ctype_cp1250_ch.result b/mysql-test/r/ctype_cp1250_ch.result
index 7f0cdf3f17b..46ca1f25ef4 100644
--- a/mysql-test/r/ctype_cp1250_ch.result
+++ b/mysql-test/r/ctype_cp1250_ch.result
@@ -238,3 +238,6 @@ select a from t1 where a like "abcdefgh
 a
 abcdefghá
 drop table t1;
+set global LC_MESSAGES=convert((@@global.log_bin_trust_function_creators) 
+using cp1250);
+ERROR HY000: Unknown system variable 'LC_MESSAGES'
diff --git a/mysql-test/r/ctype_cp1251.result b/mysql-test/r/ctype_cp1251.result
index dc12f9ceb03..2e91ecb7bc0 100644
--- a/mysql-test/r/ctype_cp1251.result
+++ b/mysql-test/r/ctype_cp1251.result
@@ -375,6 +375,8 @@ FD	FD	FD	D18D	FD
 FE	FE	FE	D18E	FE	
 FF	FF	FF	D18F	FF	
 DROP TABLE t1;
+set global LC_TIME_NAMES=convert((-8388608) using cp1251);
+ERROR HY000: Unknown locale: '-8388608'
 #
 # End of 5.1 tests
 #
diff --git a/mysql-test/r/ctype_eucjpms.result b/mysql-test/r/ctype_eucjpms.result
old mode 100755
new mode 100644
index 21aa38b7fe6..21109f596c1
--- a/mysql-test/r/ctype_eucjpms.result
+++ b/mysql-test/r/ctype_eucjpms.result
@@ -9859,3 +9859,5 @@ hex(convert(_eucjpms 0xA5FE41 using ucs2))
 select hex(convert(_eucjpms 0x8FABF841 using ucs2));
 hex(convert(_eucjpms 0x8FABF841 using ucs2))
 003F0041
+set global LC_TIME_NAMES=convert((convert((0x63) using eucjpms)) using utf8);
+ERROR HY000: Unknown locale: 'c'
diff --git a/mysql-test/t/ctype_cp1250_ch.test b/mysql-test/t/ctype_cp1250_ch.test
index 1fb656f2a01..3e17ee52164 100644
--- a/mysql-test/t/ctype_cp1250_ch.test
+++ b/mysql-test/t/ctype_cp1250_ch.test
@@ -72,3 +72,13 @@ select a from t1 where a like "abcdefgh
 drop table t1;
 
 # End of 4.1 tests
+
+#
+# Bug #48053 String::c_ptr has a race and/or does an invalid 
+#            memory reference
+#            (triggered by Valgrind tests)
+#  (see also ctype_eucjpms.test, ctype_cp1250.test, ctype_cp1251.test)
+#
+--error 1193
+set global LC_MESSAGES=convert((@@global.log_bin_trust_function_creators) 
+    using cp1250);
diff --git a/mysql-test/t/ctype_cp1251.test b/mysql-test/t/ctype_cp1251.test
index 2331c731061..bde72d04ba7 100644
--- a/mysql-test/t/ctype_cp1251.test
+++ b/mysql-test/t/ctype_cp1251.test
@@ -55,6 +55,16 @@ drop table t1;
 
 --source include/ctype_8bit.inc
 
+#
+# Bug #48053 String::c_ptr has a race and/or does an invalid 
+#            memory reference
+#            (triggered by Valgrind tests)
+#  (see also ctype_eucjpms.test, ctype_cp1250.test, ctype_cp1251.test)
+#
+--error 1105
+set global LC_TIME_NAMES=convert((-8388608) using cp1251);
+
+
 --echo #
 --echo # End of 5.1 tests
 --echo #
diff --git a/mysql-test/t/ctype_eucjpms.test b/mysql-test/t/ctype_eucjpms.test
index ec358d94900..165cfba897a 100644
--- a/mysql-test/t/ctype_eucjpms.test
+++ b/mysql-test/t/ctype_eucjpms.test
@@ -381,3 +381,11 @@ select hex(convert(_eucjpms 0xA5FE41 using ucs2));
 # the next character, which is a single byte character 0x41.
 select hex(convert(_eucjpms 0x8FABF841 using ucs2));
 
+#
+# Bug #48053 String::c_ptr has a race and/or does an invalid 
+#            memory reference
+#            (triggered by Valgrind tests)
+#  (see also ctype_eucjpms.test, ctype_cp1250.test, ctype_cp1251.test)
+#
+--error 1105
+set global LC_TIME_NAMES=convert((convert((0x63) using eucjpms)) using utf8);
diff --git a/sql/set_var.cc b/sql/set_var.cc
index d297be3fc10..26c9b06a912 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -1828,7 +1828,7 @@ bool sys_var::check_set(THD *thd, set_var *var, TYPELIB *enum_names)
     }
 
     var->save_result.ulong_value= ((ulong)
-				   find_set(enum_names, res->c_ptr(),
+				   find_set(enum_names, res->c_ptr_safe(),
 					    res->length(),
                                             NULL,
                                             &error, &error_len,
@@ -2941,7 +2941,7 @@ bool sys_var_thd_lc_time_names::check(THD *thd, set_var *var)
       my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), name, "NULL");
       return 1;
     }
-    const char *locale_str= res->c_ptr();
+    const char *locale_str= res->c_ptr_safe();
     if (!(locale_match= my_locale_by_name(locale_str)))
     {
       my_printf_error(ER_UNKNOWN_ERROR,
diff --git a/sql/sql_string.h b/sql/sql_string.h
index 092e194646f..c56c69493d4 100644
--- a/sql/sql_string.h
+++ b/sql/sql_string.h
@@ -106,6 +106,9 @@ public:
   inline const char *ptr() const { return Ptr; }
   inline char *c_ptr()
   {
+    DBUG_ASSERT(!alloced || !Ptr || !Alloced_length || 
+                (Alloced_length >= (str_length + 1)));
+
     if (!Ptr || Ptr[str_length])		/* Should be safe */
       (void) realloc(str_length);
     return Ptr;