diff --git a/libs/gtkutil/nonmodal.h b/libs/gtkutil/nonmodal.h
index 692b8b53..29f7d53a 100644
--- a/libs/gtkutil/nonmodal.h
+++ b/libs/gtkutil/nonmodal.h
@@ -39,8 +39,8 @@ public:
 		// triggered on enter & focus out; need to track editing state, as nonedited triggers this too
 		QObject::connect( this, &QLineEdit::editingFinished, [this](){
 			if( m_editing ){
-				m_apply();
 				m_editing = false;
+				m_apply();
 			}
 			clearFocus();
 		} );
@@ -80,6 +80,7 @@ public:
 	void setCallbacks( const Callback& apply, const Callback& cancel ){
 		m_apply = apply;
 		m_cancel = cancel;
+		QObject::connect( lineEdit(), &QLineEdit::textEdited, [this](){ m_editing = true; } );
 		// triggered on enter & focus out; need to track editing state, as nonedited triggers this too
 		QObject::connect( this, &QAbstractSpinBox::editingFinished, [this](){
 			if( m_editing ){
@@ -88,9 +89,6 @@ public:
 			}
 			clearFocus();
 		} );
-		QObject::connect( lineEdit(), &QLineEdit::textEdited, [this](){
-			m_editing = true;
-		} );
 	}
 	bool event( QEvent *event ) override {
 		if( event->type() == QEvent::ShortcutOverride ){
diff --git a/radiant/entityinspector.cpp b/radiant/entityinspector.cpp
index b3882e99..4e679f54 100644
--- a/radiant/entityinspector.cpp
+++ b/radiant/entityinspector.cpp
@@ -51,6 +51,7 @@
 #include <QKeyEvent>
 #include <QApplication>
 #include <QButtonGroup>
+#include <QToolTip>
 #include "gtkutil/combobox.h"
 
 #include "os/path.h"
@@ -108,6 +109,44 @@ void Scene_EntitySetKeyValue_Selected_Undoable( const char* key, const char* val
 	Scene_EntitySetKeyValue_Selected( key, value );
 }
 
+
+class KeyValueValidator : public QValidator
+{
+	QWidget *m_parent;
+public:
+	KeyValueValidator( QWidget *parent ) : QValidator( parent ), m_parent( parent ){
+	}
+	QValidator::State validate( QString& input, int &pos ) const override {
+		auto it = std::remove_if( input.begin(), input.end(), []( QChar c ){
+			return strchr( "\n\r\"", c.toLatin1() ) != nullptr;
+		} );
+		if( it != input.end() ){
+			input.chop( std::distance( it, input.end() ) );
+			QToolTip::showText( m_parent->mapToGlobal( m_parent->rect().bottomLeft() ), "No newlines & quotes are allowed in entity key values.", m_parent );
+		}
+		return QValidator::State::Acceptable;
+	}
+};
+
+class KeyNameValidator : public QValidator
+{
+	QWidget *m_parent;
+public:
+	KeyNameValidator( QWidget *parent ) : QValidator( parent ), m_parent( parent ){
+	}
+	QValidator::State validate( QString& input, int &pos ) const override {
+		auto it = std::remove_if( input.begin(), input.end(), []( QChar c ){
+			return strchr( " \n\r\t\v\"", c.toLatin1() ) != nullptr;
+		} );
+		if( it != input.end() ){
+			input.chop( std::distance( it, input.end() ) );
+			QToolTip::showText( m_parent->mapToGlobal( m_parent->rect().bottomLeft() ), "No spaces, newlines, tabs, quotes are allowed in entity key names.", m_parent );
+		}
+		return QValidator::State::Acceptable;
+	}
+};
+
+
 class EntityAttribute
 {
 public:
@@ -155,6 +194,7 @@ public:
 	StringAttribute( const char* key ) :
 		m_key( key ),
 		m_entry( new NonModalEntry( ApplyCaller( *this ), UpdateCaller( *this ) ) ){
+		m_entry->setValidator( new KeyValueValidator( m_entry ) );
 	}
 	virtual ~StringAttribute() = default;
 	QWidget* getWidget() const override {
@@ -207,6 +247,7 @@ public:
 	ColorAttribute( const char* key ) :
 		m_key( key ),
 		m_entry( new NonModalEntry( ApplyCaller( *this ), UpdateCaller( *this ) ) ){
+		m_entry->setValidator( new KeyValueValidator( m_entry ) );
 		auto button = m_entry->addAction( QApplication::style()->standardIcon( QStyle::SP_ArrowRight ), QLineEdit::ActionPosition::TrailingPosition );
 		QObject::connect( button, &QAction::triggered, [this](){ browse(); } );
 	}
@@ -245,6 +286,7 @@ public:
 	ModelAttribute( const char* key ) :
 		m_key( key ),
 		m_entry( new NonModalEntry( ApplyCaller( *this ), UpdateCaller( *this ) ) ){
+		m_entry->setValidator( new KeyValueValidator( m_entry ) );
 		auto button = m_entry->addAction( QApplication::style()->standardIcon( QStyle::SP_DialogOpenButton ), QLineEdit::ActionPosition::TrailingPosition );
 		QObject::connect( button, &QAction::triggered, [this](){ browse(); } );
 	}
@@ -308,6 +350,7 @@ public:
 	SoundAttribute( const char* key ) :
 		m_key( key ),
 		m_entry( new NonModalEntry( ApplyCaller( *this ), UpdateCaller( *this ) ) ){
+		m_entry->setValidator( new KeyValueValidator( m_entry ) );
 		auto button = m_entry->addAction( QApplication::style()->standardIcon( QStyle::SP_MediaVolume ), QLineEdit::ActionPosition::TrailingPosition );
 		QObject::connect( button, &QAction::triggered, [this](){ browse(); } );
 	}
@@ -1049,15 +1092,6 @@ void EntityInspector_applyKeyValue(){
 //		return;
 //	}
 
-	// RR2DO2: we don't want spaces and special symbols in entity keys
-	if ( std::any_of( key.cbegin(), key.cend(), []( const char c ){ return strchr( " \n\r\t\v\"", c ) != nullptr; } ) ) {
-		qt_MessageBox( g_entityKeyEntry->window(), "No spaces, newlines, tabs, quotes are allowed in entity key names." );
-		return;
-	}
-	if ( std::any_of( value.cbegin(), value.cend(), []( const char c ){ return strchr( "\n\r\"", c ) != nullptr; } ) ) {
-		qt_MessageBox( g_entityKeyEntry->window(), "No newlines & quotes are allowed in entity key values." );
-		return;
-	}
 	// avoid empty key name; empty value is okay: deletes key
 	if( key.isEmpty() )
 		return;
@@ -1247,12 +1281,14 @@ QWidget* EntityInspector_constructWindow( QWidget* toplevel ){
 				auto line = g_entityKeyEntry = new LineEdit;
 				grid->addWidget( line, 0, 1 );
 				QObject::connect( line, &QLineEdit::returnPressed, [](){ g_entityValueEntry->setFocus(); g_entityValueEntry->selectAll(); } );
+				line->setValidator( new KeyNameValidator( line ) );
 			}
 
 			{
 				auto line = g_entityValueEntry = new LineEdit;
 				grid->addWidget( line, 1, 1 );
 				QObject::connect( line, &QLineEdit::returnPressed, [](){ EntityInspector_applyKeyValue(); } );
+				line->setValidator( new KeyValueValidator( line ) );
 			}
 			/* select by key/value buttons */
 			{