diff --git a/lib/Slic3r/GUI/OptionsGroup.pm b/lib/Slic3r/GUI/OptionsGroup.pm
index efe804b2f..ac2649528 100644
--- a/lib/Slic3r/GUI/OptionsGroup.pm
+++ b/lib/Slic3r/GUI/OptionsGroup.pm
@@ -3,7 +3,7 @@ use Moo;
 
 use List::Util qw(first);
 use Wx qw(:combobox :font :misc :sizer :systemsettings :textctrl);
-use Wx::Event qw(EVT_CHECKBOX EVT_COMBOBOX EVT_SPINCTRL EVT_TEXT);
+use Wx::Event qw(EVT_CHECKBOX EVT_COMBOBOX EVT_SPINCTRL EVT_TEXT EVT_KILL_FOCUS);
 
 =head1 NAME
 
@@ -52,6 +52,7 @@ has 'label_width'   => (is => 'ro', default => sub { 180 });
 has 'extra_column'  => (is => 'ro');
 has 'label_font'    => (is => 'ro');
 has 'sidetext_font' => (is => 'ro', default => sub { Wx::SystemSettings::GetFont(wxSYS_DEFAULT_GUI_FONT) });
+has 'ignore_on_change_return' => (is => 'ro', default => sub { 1 });
 
 has 'sizer'         => (is => 'rw');
 has '_triggers'     => (is => 'ro', default => sub { {} });
@@ -166,7 +167,7 @@ sub _build_field {
     my ($opt) = @_;
     
     my $opt_key = $opt->{opt_key};
-    $self->_triggers->{$opt_key} = $opt->{on_change} || sub {};
+    $self->_triggers->{$opt_key} = $opt->{on_change} || sub { return 1 };
     
     my $field;
     my $tooltip = $opt->{tooltip};
@@ -176,11 +177,16 @@ sub _build_field {
         # default width on Windows is too large
         my $size = Wx::Size->new($opt->{width} || 60, $opt->{height} || -1);
         
-        my $on_change = sub { $self->_on_change($opt_key, $field->GetValue) };
+        my $on_change = sub {
+            my $value = $field->GetValue;
+            $value ||= 0 if $opt->{type} =~ /^(i|f|percent)$/; # prevent crash trying to pass empty strings to Config
+            $self->_on_change($opt_key, $value);
+        };
         if ($opt->{type} eq 'i') {
             $field = Wx::SpinCtrl->new($self->parent, -1, $opt->{default}, wxDefaultPosition, $size, $style, $opt->{min} || 0, $opt->{max} || 2147483647, $opt->{default});
             $self->_setters->{$opt_key} = sub { $field->SetValue($_[0]) };
             EVT_SPINCTRL ($self->parent, $field, $on_change);
+            EVT_KILL_FOCUS($field, sub { $self->on_kill_focus($opt_key) });
         } elsif ($opt->{values}) {
             $field = Wx::ComboBox->new($self->parent, -1, $opt->{default}, wxDefaultPosition, $size, $opt->{labels} || $opt->{values});
             $self->_setters->{$opt_key} = sub {
@@ -191,10 +197,12 @@ sub _build_field {
                 $self->_on_change($opt_key, $on_change);
             });
             EVT_TEXT($self->parent, $field, $on_change);
+            EVT_KILL_FOCUS($field, sub { $self->on_kill_focus($opt_key) });
         } else {
             $field = Wx::TextCtrl->new($self->parent, -1, $opt->{default}, wxDefaultPosition, $size, $style);
             $self->_setters->{$opt_key} = sub { $field->ChangeValue($_[0]) };
-            EVT_TEXT ($self->parent, $field, $on_change);
+            EVT_TEXT($self->parent, $field, $on_change);
+            EVT_KILL_FOCUS($field, sub { $self->on_kill_focus($opt_key) });
         }
         $field->Disable if $opt->{readonly};
         $tooltip .= " (default: " . $opt->{default} .  ")" if ($opt->{default});
@@ -220,8 +228,10 @@ sub _build_field {
                 $tooltip . " (default: " .  join(",", @{$opt->{default}}) .  ")"
             ) for @items;
         }
-        EVT_TEXT($self->parent, $_, sub { $self->_on_change($opt_key, [ $x_field->GetValue, $y_field->GetValue ]) })
-            for $x_field, $y_field;
+        foreach my $field ($x_field, $y_field) {
+            EVT_TEXT($self->parent, $field, sub { $self->_on_change($opt_key, [ $x_field->GetValue, $y_field->GetValue ]) });
+            EVT_KILL_FOCUS($field, sub { $self->on_kill_focus($opt_key) });
+        }
         $self->_setters->{$opt_key} = sub {
             $x_field->SetValue($_[0][0]);
             $y_field->SetValue($_[0][1]);
@@ -260,7 +270,7 @@ sub _on_change {
     my ($opt_key, $value) = @_;
     
     return if $self->sizer->GetStaticBox->GetParent->{disabled};
-    $self->_triggers->{$opt_key}->($value);
+    $self->_triggers->{$opt_key}->($value) or $self->ignore_on_change_return or return;
     $self->on_change->($opt_key, $value);
 }
 
@@ -285,6 +295,8 @@ sub set_value {
     return 0;
 }
 
+sub on_kill_focus {}
+
 package Slic3r::GUI::ConfigOptionsGroup;
 use Moo;
 
@@ -313,6 +325,7 @@ use List::Util qw(first);
 
 has 'config' => (is => 'ro', required => 1);
 has 'full_labels' => (is => 'ro', default => sub {0});
+has '+ignore_on_change_return' => (is => 'ro', default => sub { 0 });
 
 sub _trigger_options {
     my $self = shift;
@@ -323,13 +336,17 @@ sub _trigger_options {
             my $full_key = $opt;
             my ($opt_key, $index) = $self->_split_key($full_key);
             my $config_opt = $Slic3r::Config::Options->{$opt_key};
+            
+            my $default = $config_opt->{default};
+            $default = $default->[$index] if defined($index) && $index <= $#$default;
+            
             $opt = {
                 opt_key     => $full_key,
                 config      => 1,
                 label       => ($self->full_labels && defined $config_opt->{full_label}) ? $config_opt->{full_label} : $config_opt->{label},
                 (map { $_   => $config_opt->{$_} } qw(type tooltip sidetext width height full_width min max labels values multiline readonly)),
-                default     => $self->_get_config($opt_key, $index),
-                on_change   => sub { $self->_set_config($opt_key, $index, $_[0]) },
+                default     => $default,
+                on_change   => sub { return $self->_set_config($opt_key, $index, $_[0]) },
             };
         }
         $opt;
@@ -367,6 +384,16 @@ sub set_value {
     return $changed;
 }
 
+sub on_kill_focus {
+    my ($self, $full_key) = @_;
+    
+    # when a field loses focus, reapply the config value to it
+    # (thus discarding any invalid input and reverting to the last
+    # accepted value)
+    my ($key, $index) = $self->_split_key($full_key);
+    $self->SUPER::set_value($full_key, $self->_get_config($key, $index));
+}
+
 sub _split_key {
     my $self = shift;
     my ($opt_key) = @_;
@@ -378,10 +405,10 @@ sub _split_key {
 
 sub _get_config {
     my $self = shift;
-    my ($opt_key, $index) = @_;
+    my ($opt_key, $index, $config) = @_;
     
     my ($get_m, $serialized) = $self->_config_methods($opt_key, $index);
-    my $value = $self->config->$get_m($opt_key);
+    my $value = ($config // $self->config)->$get_m($opt_key);
     if (defined $index) {
         $value->[$index] //= $value->[0]; #/
         $value = $value->[$index];
@@ -400,9 +427,9 @@ sub _set_config {
         $self->config->set($opt_key, $values);
     } else {
         if ($serialized) {
-            $self->config->set_deserialize($opt_key, $value);
+            return $self->config->set_deserialize($opt_key, $value);
         } else {
-            $self->config->set($opt_key, $value);
+            return $self->config->set($opt_key, $value);
         }
     }
 }
diff --git a/xs/src/Config.cpp b/xs/src/Config.cpp
index de99b96ec..7c3280d5f 100644
--- a/xs/src/Config.cpp
+++ b/xs/src/Config.cpp
@@ -33,19 +33,20 @@ ConfigBase::serialize(const t_config_option_key opt_key) {
     return opt->serialize();
 }
 
-void
+bool
 ConfigBase::set_deserialize(const t_config_option_key opt_key, std::string str) {
     if (this->def->count(opt_key) == 0) throw "Calling set_deserialize() on unknown option";
     ConfigOptionDef* optdef = &(*this->def)[opt_key];
     if (!optdef->shortcut.empty()) {
-        for (std::vector<t_config_option_key>::iterator it = optdef->shortcut.begin(); it != optdef->shortcut.end(); ++it)
-            this->set_deserialize(*it, str);
-        return;
+        for (std::vector<t_config_option_key>::iterator it = optdef->shortcut.begin(); it != optdef->shortcut.end(); ++it) {
+            if (!this->set_deserialize(*it, str)) return false;
+        }
+        return true;
     }
     
     ConfigOption* opt = this->option(opt_key, true);
     assert(opt != NULL);
-    opt->deserialize(str);
+    return opt->deserialize(str);
 }
 
 double
@@ -164,31 +165,37 @@ ConfigBase::get_at(t_config_option_key opt_key, size_t i) {
     }
 }
 
-void
+bool
 ConfigBase::set(t_config_option_key opt_key, SV* value) {
     ConfigOption* opt = this->option(opt_key, true);
     if (opt == NULL) CONFESS("Trying to set non-existing option");
     
     if (ConfigOptionFloat* optv = dynamic_cast<ConfigOptionFloat*>(opt)) {
+        if (!looks_like_number(value)) return false;
         optv->value = SvNV(value);
     } else if (ConfigOptionFloats* optv = dynamic_cast<ConfigOptionFloats*>(opt)) {
-        optv->values.clear();
+        std::vector<double> values;
         AV* av = (AV*)SvRV(value);
         const size_t len = av_len(av)+1;
         for (size_t i = 0; i < len; i++) {
             SV** elem = av_fetch(av, i, 0);
-            optv->values.push_back(SvNV(*elem));
+            if (!looks_like_number(*elem)) return false;
+            values.push_back(SvNV(*elem));
         }
+        optv->values = values;
     } else if (ConfigOptionInt* optv = dynamic_cast<ConfigOptionInt*>(opt)) {
+        if (!looks_like_number(value)) return false;
         optv->value = SvIV(value);
     } else if (ConfigOptionInts* optv = dynamic_cast<ConfigOptionInts*>(opt)) {
-        optv->values.clear();
+        std::vector<int> values;
         AV* av = (AV*)SvRV(value);
         const size_t len = av_len(av)+1;
         for (size_t i = 0; i < len; i++) {
             SV** elem = av_fetch(av, i, 0);
-            optv->values.push_back(SvIV(*elem));
+            if (!looks_like_number(*elem)) return false;
+            values.push_back(SvIV(*elem));
         }
+        optv->values = values;
     } else if (ConfigOptionString* optv = dynamic_cast<ConfigOptionString*>(opt)) {
         optv->value = std::string(SvPV_nolen(value), SvCUR(value));
     } else if (ConfigOptionStrings* optv = dynamic_cast<ConfigOptionStrings*>(opt)) {
@@ -200,17 +207,18 @@ ConfigBase::set(t_config_option_key opt_key, SV* value) {
             optv->values.push_back(std::string(SvPV_nolen(*elem), SvCUR(*elem)));
         }
     } else if (ConfigOptionPoint* optv = dynamic_cast<ConfigOptionPoint*>(opt)) {
-        optv->point.from_SV(value);
+        return optv->point.from_SV(value);
     } else if (ConfigOptionPoints* optv = dynamic_cast<ConfigOptionPoints*>(opt)) {
-        optv->values.clear();
+        std::vector<Pointf> values;
         AV* av = (AV*)SvRV(value);
         const size_t len = av_len(av)+1;
         for (size_t i = 0; i < len; i++) {
             SV** elem = av_fetch(av, i, 0);
             Pointf point;
-            point.from_SV(*elem);
-            optv->values.push_back(point);
+            if (!point.from_SV(*elem)) return false;
+            values.push_back(point);
         }
+        optv->values = values;
     } else if (ConfigOptionBool* optv = dynamic_cast<ConfigOptionBool*>(opt)) {
         optv->value = SvTRUE(value);
     } else if (ConfigOptionBools* optv = dynamic_cast<ConfigOptionBools*>(opt)) {
@@ -222,8 +230,9 @@ ConfigBase::set(t_config_option_key opt_key, SV* value) {
             optv->values.push_back(SvTRUE(*elem));
         }
     } else {
-        opt->deserialize( std::string(SvPV_nolen(value)) );
+        if (!opt->deserialize( std::string(SvPV_nolen(value)) )) return false;
     }
+    return true;
 }
 #endif
 
@@ -347,16 +356,17 @@ StaticConfig::option(const t_config_option_key opt_key) const
 }
 
 #ifdef SLIC3RXS
-void
+bool
 StaticConfig::set(t_config_option_key opt_key, SV* value) {
     ConfigOptionDef* optdef = &(*this->def)[opt_key];
     if (!optdef->shortcut.empty()) {
-        for (std::vector<t_config_option_key>::iterator it = optdef->shortcut.begin(); it != optdef->shortcut.end(); ++it)
-            this->set(*it, value);
-        return;
+        for (std::vector<t_config_option_key>::iterator it = optdef->shortcut.begin(); it != optdef->shortcut.end(); ++it) {
+            if (!this->set(*it, value)) return false;
+        }
+        return true;
     }
     
-    static_cast<ConfigBase*>(this)->set(opt_key, value);
+    return static_cast<ConfigBase*>(this)->set(opt_key, value);
 }
 #endif
 
diff --git a/xs/src/Config.hpp b/xs/src/Config.hpp
index 226ebe7a9..5b4cb8284 100644
--- a/xs/src/Config.hpp
+++ b/xs/src/Config.hpp
@@ -21,7 +21,7 @@ class ConfigOption {
     public:
     virtual ~ConfigOption() {};
     virtual std::string serialize() const = 0;
-    virtual void deserialize(std::string str) = 0;
+    virtual bool deserialize(std::string str) = 0;
 };
 
 template <class T>
@@ -54,8 +54,9 @@ class ConfigOptionFloat : public ConfigOption
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->value = ::atof(str.c_str());
+        return true;
     };
 };
 
@@ -72,13 +73,14 @@ class ConfigOptionFloats : public ConfigOption, public ConfigOptionVector<double
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->values.clear();
         std::istringstream is(str);
         std::string item_str;
         while (std::getline(is, item_str, ',')) {
             this->values.push_back(::atof(item_str.c_str()));
         }
+        return true;
     };
 };
 
@@ -96,8 +98,9 @@ class ConfigOptionInt : public ConfigOption
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->value = ::atoi(str.c_str());
+        return true;
     };
 };
 
@@ -114,13 +117,14 @@ class ConfigOptionInts : public ConfigOption, public ConfigOptionVector<int>
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->values.clear();
         std::istringstream is(str);
         std::string item_str;
         while (std::getline(is, item_str, ',')) {
             this->values.push_back(::atoi(item_str.c_str()));
         }
+        return true;
     };
 };
 
@@ -145,7 +149,7 @@ class ConfigOptionString : public ConfigOption
         return str; 
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         // s/\\n/\n/g
         size_t pos = 0;
         while ((pos = str.find("\\n", pos)) != std::string::npos) {
@@ -154,6 +158,7 @@ class ConfigOptionString : public ConfigOption
         }
         
         this->value = str;
+        return true;
     };
 };
 
@@ -171,13 +176,14 @@ class ConfigOptionStrings : public ConfigOption, public ConfigOptionVector<std::
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->values.clear();
         std::istringstream is(str);
         std::string item_str;
         while (std::getline(is, item_str, ';')) {
             this->values.push_back(item_str);
         }
+        return true;
     };
 };
 
@@ -199,9 +205,10 @@ class ConfigOptionPercent : public ConfigOption
         return s;
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         // don't try to parse the trailing % since it's optional
-        sscanf(str.c_str(), "%lf", &this->value);
+        int res = sscanf(str.c_str(), "%lf", &this->value);
+        return res == 1;
     };
 };
 
@@ -228,14 +235,16 @@ class ConfigOptionFloatOrPercent : public ConfigOption
         return s;
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         if (str.find_first_of("%") != std::string::npos) {
-            sscanf(str.c_str(), "%lf%%", &this->value);
+            int res = sscanf(str.c_str(), "%lf%%", &this->value);
+            if (res == 0) return false;
             this->percent = true;
         } else {
             this->value = ::atof(str.c_str());
             this->percent = false;
         }
+        return true;
     };
 };
 
@@ -255,8 +264,9 @@ class ConfigOptionPoint : public ConfigOption
         return ss.str();
     };
     
-    void deserialize(std::string str) {
-        sscanf(str.c_str(), "%lf%*1[,x]%lf", &this->point.x, &this->point.y);
+    bool deserialize(std::string str) {
+        int res = sscanf(str.c_str(), "%lf%*1[,x]%lf", &this->point.x, &this->point.y);
+        return res == 2;
     };
 };
 
@@ -275,15 +285,17 @@ class ConfigOptionPoints : public ConfigOption, public ConfigOptionVector<Pointf
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->values.clear();
         std::istringstream is(str);
         std::string point_str;
         while (std::getline(is, point_str, ',')) {
             Pointf point;
-            sscanf(point_str.c_str(), "%lfx%lf", &point.x, &point.y);
+            int res = sscanf(point_str.c_str(), "%lfx%lf", &point.x, &point.y);
+            if (res != 2) return false;
             this->values.push_back(point);
         }
+        return true;
     };
 };
 
@@ -299,8 +311,9 @@ class ConfigOptionBool : public ConfigOption
         return std::string(this->value ? "1" : "0");
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->value = (str.compare("1") == 0);
+        return true;
     };
 };
 
@@ -317,13 +330,14 @@ class ConfigOptionBools : public ConfigOption, public ConfigOptionVector<bool>
         return ss.str();
     };
     
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         this->values.clear();
         std::istringstream is(str);
         std::string item_str;
         while (std::getline(is, item_str, ',')) {
             this->values.push_back(item_str.compare("1") == 0);
         }
+        return true;
     };
 };
 
@@ -345,10 +359,11 @@ class ConfigOptionEnum : public ConfigOption
         return "";
     };
 
-    void deserialize(std::string str) {
+    bool deserialize(std::string str) {
         t_config_enum_values enum_keys_map = ConfigOptionEnum<T>::get_enum_values();
-        assert(enum_keys_map.count(str) > 0);
+        if (enum_keys_map.count(str) == 0) return false;
         this->value = static_cast<T>(enum_keys_map[str]);
+        return true;
     };
 
     static t_config_enum_values get_enum_values();
@@ -371,9 +386,10 @@ class ConfigOptionEnumGeneric : public ConfigOption
         return "";
     };
 
-    void deserialize(std::string str) {
-        assert(this->keys_map->count(str) != 0);
+    bool deserialize(std::string str) {
+        if (this->keys_map->count(str) == 0) return false;
         this->value = (*this->keys_map)[str];
+        return true;
     };
 };
 
@@ -435,7 +451,7 @@ class ConfigBase
     virtual void keys(t_config_option_keys *keys) const = 0;
     void apply(const ConfigBase &other, bool ignore_nonexistent = false);
     std::string serialize(const t_config_option_key opt_key);
-    void set_deserialize(const t_config_option_key opt_key, std::string str);
+    bool set_deserialize(const t_config_option_key opt_key, std::string str);
     double get_abs_value(const t_config_option_key opt_key);
     double get_abs_value(const t_config_option_key opt_key, double ratio_over);
     
@@ -443,7 +459,7 @@ class ConfigBase
     SV* as_hash();
     SV* get(t_config_option_key opt_key);
     SV* get_at(t_config_option_key opt_key, size_t i);
-    void set(t_config_option_key opt_key, SV* value);
+    bool set(t_config_option_key opt_key, SV* value);
     #endif
 };
 
@@ -477,7 +493,7 @@ class StaticConfig : public ConfigBase
     const ConfigOption* option(const t_config_option_key opt_key) const;
     
     #ifdef SLIC3RXS
-    void set(t_config_option_key opt_key, SV* value);
+    bool set(t_config_option_key opt_key, SV* value);
     #endif
 };
 
diff --git a/xs/src/Point.cpp b/xs/src/Point.cpp
index 57385a9d4..a6c844054 100644
--- a/xs/src/Point.cpp
+++ b/xs/src/Point.cpp
@@ -201,12 +201,17 @@ Pointf::to_SV_pureperl() const {
     return newRV_noinc((SV*)av);
 }
 
-void
+bool
 Pointf::from_SV(SV* point_sv)
 {
     AV* point_av = (AV*)SvRV(point_sv);
-    this->x = SvNV(*av_fetch(point_av, 0, 0));
-    this->y = SvNV(*av_fetch(point_av, 1, 0));
+    SV* sv_x = *av_fetch(point_av, 0, 0);
+    SV* sv_y = *av_fetch(point_av, 1, 0);
+    if (!looks_like_number(sv_x) || !looks_like_number(sv_x)) return false;
+    
+    this->x = SvNV(sv_x);
+    this->y = SvNV(sv_y);
+    return true;
 }
 #endif
 
diff --git a/xs/src/Point.hpp b/xs/src/Point.hpp
index 8fb0ab0bf..8f3cec554 100644
--- a/xs/src/Point.hpp
+++ b/xs/src/Point.hpp
@@ -66,7 +66,7 @@ class Pointf
     void translate(double x, double y);
     
     #ifdef SLIC3RXS
-    void from_SV(SV* point_sv);
+    bool from_SV(SV* point_sv);
     SV* to_SV_pureperl() const;
     #endif
 };
diff --git a/xs/src/PrintConfig.hpp b/xs/src/PrintConfig.hpp
index 46ed6c790..49cc64067 100644
--- a/xs/src/PrintConfig.hpp
+++ b/xs/src/PrintConfig.hpp
@@ -228,6 +228,7 @@ class PrintConfigDef
         Options["fan_below_layer_time"].sidetext = "approximate seconds";
         Options["fan_below_layer_time"].cli = "fan-below-layer-time=i";
         Options["fan_below_layer_time"].width = 60;
+        Options["fan_below_layer_time"].min = 0;
         Options["fan_below_layer_time"].max = 1000;
 
         Options["filament_diameter"].type = coFloats;
@@ -235,6 +236,7 @@ class PrintConfigDef
         Options["filament_diameter"].tooltip = "Enter your filament diameter here. Good precision is required, so use a caliper and do multiple measurements along the filament, then compute the average.";
         Options["filament_diameter"].sidetext = "mm";
         Options["filament_diameter"].cli = "filament-diameter=f@";
+        Options["filament_diameter"].min = 0;
 
         Options["fill_angle"].type = coInt;
         Options["fill_angle"].label = "Fill angle";
@@ -242,6 +244,7 @@ class PrintConfigDef
         Options["fill_angle"].tooltip = "Default base angle for infill orientation. Cross-hatching will be applied to this. Bridges will be infilled using the best direction Slic3r can detect, so this setting does not affect them.";
         Options["fill_angle"].sidetext = "°";
         Options["fill_angle"].cli = "fill-angle=i";
+        Options["fill_angle"].min = 0;
         Options["fill_angle"].max = 359;
 
         Options["fill_density"].type = coPercent;
diff --git a/xs/xsp/Config.xsp b/xs/xsp/Config.xsp
index 7b611b39e..61490f967 100644
--- a/xs/xsp/Config.xsp
+++ b/xs/xsp/Config.xsp
@@ -12,8 +12,8 @@
     SV* as_hash();
     SV* get(t_config_option_key opt_key);
     SV* get_at(t_config_option_key opt_key, int i);
-    void set(t_config_option_key opt_key, SV* value);
-    void set_deserialize(t_config_option_key opt_key, std::string str);
+    bool set(t_config_option_key opt_key, SV* value);
+    bool set_deserialize(t_config_option_key opt_key, std::string str);
     std::string serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}
@@ -34,8 +34,8 @@
     SV* as_hash();
     SV* get(t_config_option_key opt_key);
     SV* get_at(t_config_option_key opt_key, int i);
-    void set(t_config_option_key opt_key, SV* value);
-    void set_deserialize(t_config_option_key opt_key, std::string str);
+    bool set(t_config_option_key opt_key, SV* value);
+    bool set_deserialize(t_config_option_key opt_key, std::string str);
     std::string serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}
@@ -54,8 +54,8 @@
     SV* as_hash();
     SV* get(t_config_option_key opt_key);
     SV* get_at(t_config_option_key opt_key, int i);
-    void set(t_config_option_key opt_key, SV* value);
-    void set_deserialize(t_config_option_key opt_key, std::string str);
+    bool set(t_config_option_key opt_key, SV* value);
+    bool set_deserialize(t_config_option_key opt_key, std::string str);
     std::string serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}
@@ -75,8 +75,8 @@
     SV* as_hash();
     SV* get(t_config_option_key opt_key);
     SV* get_at(t_config_option_key opt_key, int i);
-    void set(t_config_option_key opt_key, SV* value);
-    void set_deserialize(t_config_option_key opt_key, std::string str);
+    bool set(t_config_option_key opt_key, SV* value);
+    bool set_deserialize(t_config_option_key opt_key, std::string str);
     std::string serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}
@@ -96,8 +96,8 @@
     SV* as_hash();
     SV* get(t_config_option_key opt_key);
     SV* get_at(t_config_option_key opt_key, int i);
-    void set(t_config_option_key opt_key, SV* value);
-    void set_deserialize(t_config_option_key opt_key, std::string str);
+    bool set(t_config_option_key opt_key, SV* value);
+    bool set_deserialize(t_config_option_key opt_key, std::string str);
     std::string serialize(t_config_option_key opt_key);
     double get_abs_value(t_config_option_key opt_key);
     %name{get_abs_value_over}