diff --git a/mysql-test/r/flagset_option_with_unrecognized_flag.result b/mysql-test/r/flagset_option_with_unrecognized_flag.result
index 6ceacdb93ac..db2dd81e8e9 100644
--- a/mysql-test/r/flagset_option_with_unrecognized_flag.result
+++ b/mysql-test/r/flagset_option_with_unrecognized_flag.result
@@ -22,4 +22,6 @@ Warnings:
 Warning	6424	Adjusted incorrect optimizer_switch value: 'ab=c=-d=123-,', discarding 'ab=c=-d=123-'.
 SET optimizer_switch='mrr=on';
 SET optimizer_switch='';
+SET optimizer_switch='index';
+ERROR 42000: Variable 'optimizer_switch' can't be set to the value of 'index'
 # restart:
diff --git a/mysql-test/t/flagset_option_with_unrecognized_flag.test b/mysql-test/t/flagset_option_with_unrecognized_flag.test
index 786f05ca07a..f85f14cc8fa 100644
--- a/mysql-test/t/flagset_option_with_unrecognized_flag.test
+++ b/mysql-test/t/flagset_option_with_unrecognized_flag.test
@@ -24,6 +24,9 @@ SET optimizer_switch='mrr=on,ab=c=-d=123-,derived_merge=off';
 SET optimizer_switch='ab=c=-d=123-,';
 SET optimizer_switch='mrr=on';
 SET optimizer_switch='';
+# Coverage test for any true error which are not adjusted.
+--error ER_WRONG_VALUE_FOR_VAR
+SET optimizer_switch='index';
 
 let $restart_parameters = "restart:";
 --source include/restart_mysqld.inc
diff --git a/mysys/my_getopt.cc b/mysys/my_getopt.cc
index b5bbb9831fb..3f372108748 100644
--- a/mysys/my_getopt.cc
+++ b/mysys/my_getopt.cc
@@ -956,17 +956,17 @@ static int setval(const struct my_option *opts, void *value,
             strlen(argument), &flag_error, &error_len, abuf, sizeof(abuf),
             ebuf, sizeof(ebuf));
 
+        if (flag_error) {
+          res = EXIT_ARGUMENT_INVALID;
+          goto ret;
+        };
+
         if (ebuf[0] != '\0') {
           my_getopt_error_reporter(
               WARNING_LEVEL, EE_ADJUSTED_FLAGSET_VALUE_FOR_OPTION, opts->name,
               argument, abuf, ebuf);
           assert(!flag_error);
         }
-
-        if (flag_error) {
-          res = EXIT_ARGUMENT_INVALID;
-          goto ret;
-        };
       } break;
       case GET_NO_ARG: /* get_one_option has taken care of the value already */
       default:         /* dummy default to avoid compiler warnings */
diff --git a/mysys/typelib.cc b/mysys/typelib.cc
index 981d33e308e..659fdd45331 100644
--- a/mysys/typelib.cc
+++ b/mysys/typelib.cc
@@ -296,7 +296,8 @@ inline void append_flag(char *buf, uint size, char **pp, const char *start,
   @param err_len      OUT  If error, set to the length of wrong set string
   @param abuf         OUT  String buffer to collect recognized flags
   @param asize             Size of abuf
-  @param ebuf         OUT  String buffer to collect unrecognized flags
+  @param ebuf         OUT  String buffer to collect unrecognized flags (they are
+                           not errors, thus should be checked on success)
   @param esize             Size of ebuf
 
   @details
diff --git a/sql/set_var.cc b/sql/set_var.cc
index fbb32228673..4e7817afb5b 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -591,10 +591,10 @@ bool throw_bounds_warning(THD *thd, const char *name, bool fixed, double v) {
 }
 
 bool throw_bounds_warning(THD *thd, const char *name, bool fixed,
-                          const char *v, const char *err, const char *eb) {
+                          const char *v, const char *eb) {
   if (fixed) {
     if (thd->variables.sql_mode & MODE_STRICT_ALL_TABLES) {
-      my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), name, err);
+      my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), name, eb);
       return true;
     }
     push_warning_printf(thd, Sql_condition::SL_WARNING,
diff --git a/sql/sys_vars.h b/sql/sys_vars.h
index 01d9b3f881b..c8f828287ae 100644
--- a/sql/sys_vars.h
+++ b/sql/sys_vars.h
@@ -1567,16 +1567,17 @@ class Sys_var_flagset : public Sys_var_typelib {
             &typelib, typelib.count, current_value, default_value, res->ptr(),
             static_cast<uint>(res->length()), &error, &error_len,
             abuf, sizeof(abuf), ebuf, sizeof(ebuf));
-        if (!error) {
-          error = ebuf;
-          error_len = strlen(ebuf);
-        }
-        const ErrConvString err(error, error_len, res->charset());
-        const ErrConvString eb(ebuf, strlen(ebuf), res->charset());
+        if (error) {
+          const ErrConvString err(error, error_len, res->charset());
+          my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), name.str, err.ptr());
+          return true;
+	}
 
+        const ErrConvString eb(ebuf, strlen(ebuf), res->charset());
         bool fixed = ebuf[0] != '\0';
-        return throw_bounds_warning(current_thd, name.str, fixed, res->ptr(),
-                                    err.ptr(), eb.ptr());
+        if (throw_bounds_warning(current_thd, name.str, fixed, res->ptr(),
+                                 eb.ptr()))
+          return true;
       }
     } else {
       const longlong tmp = var->value->val_int();
diff --git a/sql/sys_vars_shared.h b/sql/sys_vars_shared.h
index 56f91fcfd5f..2743bc502ff 100644
--- a/sql/sys_vars_shared.h
+++ b/sql/sys_vars_shared.h
@@ -45,8 +45,7 @@ extern bool throw_bounds_warning(THD *thd, const char *name, bool fixed,
 extern bool throw_bounds_warning(THD *thd, const char *name, bool fixed,
                                  double v);
 extern bool throw_bounds_warning(THD *thd, const char *name, bool fixed,
-                                 const char *v, const char *err,
-                                 const char *eb);
+                                 const char *v, const char *eb);
 extern sys_var *find_static_system_variable(const std::string &name);
 extern sys_var *find_dynamic_system_variable(const std::string &name);
 extern sys_var *intern_find_sys_var(const char *str, size_t length);