diff --git a/src/frontends/controllers/ChangeLog b/src/frontends/controllers/ChangeLog
index ae17a736fa..ffd2cc4c7a 100644
--- a/src/frontends/controllers/ChangeLog
+++ b/src/frontends/controllers/ChangeLog
@@ -1,3 +1,9 @@
+2005-05-13  Angus Leeming  <leeming@lyx.org>
+
+	* helper_funcs.C (browseFile, browseDir): remove the loop that tested
+	whether the returned file name is valid in order to break out of the
+	loop.
+
 2005-05-08  Angus Leeming  <leeming@lyx.org>
 
 	* Kernel.h (KernelDocType): wrapper class for the Kernel::DocTypes
diff --git a/src/frontends/controllers/helper_funcs.C b/src/frontends/controllers/helper_funcs.C
index aafd5f3537..582d88820f 100644
--- a/src/frontends/controllers/helper_funcs.C
+++ b/src/frontends/controllers/helper_funcs.C
@@ -16,10 +16,10 @@
 
 #include "gettext.h"
 
-#include "frontends/Alert.h"
 #include "frontends/FileDialog.h"
 
 #include "support/filetools.h"
+#include "support/lstrings.h"
 #include "support/package.h"
 
 using std::pair;
@@ -61,27 +61,12 @@ string const browseFile(string const & filename,
 
 	FileDialog::Result result;
 
-	while (true) {
-		if (save)
-			result = fileDlg.save(lastPath, filters,
-				OnlyFilename(filename));
-		else
-			result = fileDlg.open(lastPath, filters,
-				OnlyFilename(filename));
-
-		if (result.second.empty())
-			return result.second;
-
-		lastPath = OnlyPath(result.second);
-
-		if (result.second.find_first_of("#~$% ") == string::npos)
-			break;
-
-		Alert::error(_("Invalid filename"),
-			_("Filename can't contain any "
-			"of these characters:\n"
-			"space, '#', '~', '$' or '%'."));
-	}
+	if (save)
+		result = fileDlg.save(lastPath, filters,
+				      OnlyFilename(filename));
+	else
+		result = fileDlg.open(lastPath, filters,
+				      OnlyFilename(filename));
 
 	return result.second;
 }
@@ -150,25 +135,8 @@ string const browseDir(string const & pathname,
 
 	FileDialog fileDlg(title, LFUN_SELECT_FILE_SYNC, dir1, dir2);
 
-	FileDialog::Result result;
-
-	while (true) {
-		result = fileDlg.opendir(lastPath,
-				OnlyFilename(pathname));
-
-		if (result.second.empty())
-			return result.second;
-
-		lastPath = OnlyPath(result.second);
-
-		if (result.second.find_first_of("#~$% ") == string::npos)
-			break;
-
-		Alert::error(_("Invalid filename"),
-			_("Filename can't contain any "
-			"of these characters:\n"
-			"space, '#', '~', '$' or '%'."));
-	}
+	FileDialog::Result const result =
+		fileDlg.opendir(lastPath, OnlyFilename(pathname));
 
 	return result.second;
 }
diff --git a/src/frontends/qt2/ChangeLog b/src/frontends/qt2/ChangeLog
index 58398bbb5d..80124a9915 100644
--- a/src/frontends/qt2/ChangeLog
+++ b/src/frontends/qt2/ChangeLog
@@ -1,3 +1,22 @@
+2005-05-13  Angus Leeming  <leeming@lyx.org>
+
+	* QBibtex.C (build_dialog):
+	* QBibtexDialog.C (c-tor, bibEDChanged, addPressed): add a
+	PathValidator of the add_->BibED widget and use it to control
+	the activation state of the "Add" button.
+
+	* QExternal.C (build_dialog, update_contents):
+	* QExternalDialog.C (c-tor): add a PathValidator of the fileED
+	widget.
+
+	* QGraphics.C (build_dialog, update_contents):
+	* QGraphicsDialog.C (c-tor): add a PathValidator of the filename
+	widget.
+
+	* QInclude.C (build_dialog, update_contents):
+	* QIncludeDialog.C (c-tor): add a PathValidator of the filenameED
+	widget.
+
 2005-05-09  Michael Schmitt  <michael.schmitt@teststep.org>
 
 	* *.C: strip "LyX: " prefix from dialog titles; harmonize
diff --git a/src/frontends/qt2/QBibtex.C b/src/frontends/qt2/QBibtex.C
index 482fb3a7da..feb7bbc9ad 100644
--- a/src/frontends/qt2/QBibtex.C
+++ b/src/frontends/qt2/QBibtex.C
@@ -17,6 +17,9 @@
 #include "ui/QBibtexAddDialogBase.h"
 #include "Qt2BC.h"
 #include "qt_helpers.h"
+#include "validators.h"
+
+#include "lyxrc.h"
 
 #include "controllers/ControlBibtex.h"
 
@@ -66,6 +69,11 @@ void QBibtex::build_dialog()
 
 void QBibtex::update_contents()
 {
+	PathValidator * path_validator =
+		getPathValidator(dialog_->add_->bibED);
+	if (path_validator)
+		path_validator->setChecker(kernel().docType(), lyxrc);
+
 	bool bibtopic = controller().usingBibtopic();
 
 	dialog_->databaseLB->clear();
diff --git a/src/frontends/qt2/QBibtexDialog.C b/src/frontends/qt2/QBibtexDialog.C
index 5b4ef22ac3..4f93cf7685 100644
--- a/src/frontends/qt2/QBibtexDialog.C
+++ b/src/frontends/qt2/QBibtexDialog.C
@@ -13,10 +13,17 @@
 #include "QBibtexDialog.h"
 #include "ui/QBibtexAddDialogBase.h"
 #include "QBibtex.h"
+
+#include "checkedwidgets.h"
+#include "Qt2BC.h"
 #include "qt_helpers.h"
+#include "validators.h"
 
 #include "controllers/ControlBibtex.h"
+#include "controllers/ButtonPolicies.h"
+
 #include "support/filetools.h"
+#include "support/lstrings.h"
 
 #include <qpushbutton.h>
 #include <qcombobox.h>
@@ -24,6 +31,7 @@
 #include <qlistbox.h>
 
 using lyx::support::ChangeExtension;
+using lyx::support::trim;
 
 using std::string;
 
@@ -40,12 +48,41 @@ QBibtexDialog::QBibtexDialog(QBibtex * form)
 		form, SLOT(slotClose()));
 
 	add_ = new QBibtexAddDialogBase(this, "", true);
-	connect(add_->addPB, SIGNAL(clicked()), this, SLOT(addDatabase()));
-	connect(add_->addPB, SIGNAL(clicked()), this, SLOT(addDatabase()));
-	connect(add_->bibLB, SIGNAL(selected(QListBoxItem *)), this, SLOT(addDatabase()));
-	connect(add_->bibLB, SIGNAL(selected(QListBoxItem *)), add_, SLOT(accept()));
-	connect(add_->bibLB, SIGNAL(currentChanged(QListBoxItem *)), this, SLOT(availableChanged()));
-	connect(add_->browsePB, SIGNAL(clicked()), this, SLOT(browseBibPressed()));
+	Qt2BC * bcview = new Qt2BC(add_bc_);
+	add_bc_.view(bcview);
+	add_bc_.bp(new OkCancelPolicy);
+
+	bcview->setOK(add_->addPB);
+	bcview->setCancel(add_->closePB);
+
+	add_->bibED->setValidator(new PathValidator(false, add_->bibED));
+	addCheckedLineEdit(add_bc_.view(), add_->bibED, 0);
+
+	connect(add_->bibED, SIGNAL(textChanged(const QString&)),
+		this, SLOT(bibEDChanged()));
+	connect(add_->addPB, SIGNAL(clicked()),
+		this, SLOT(addDatabase()));
+	connect(add_->bibLB, SIGNAL(selected(QListBoxItem *)),
+		this, SLOT(addDatabase()));
+	connect(add_->bibLB, SIGNAL(selected(QListBoxItem *)),
+		add_, SLOT(accept()));
+	connect(add_->bibLB, SIGNAL(currentChanged(QListBoxItem *)),
+		this, SLOT(availableChanged()));
+	connect(add_->browsePB, SIGNAL(clicked()),
+		this, SLOT(browseBibPressed()));
+}
+
+
+QBibtexDialog::~QBibtexDialog()
+{}
+
+
+void QBibtexDialog::bibEDChanged()
+{
+	// Indicate to the button controller that the contents have
+	// changed. The actual test of validity is carried out by
+	// the checkedLineEdit.
+	add_bc_.valid(true);
 }
 
 
@@ -82,7 +119,7 @@ void QBibtexDialog::browsePressed()
 
 void QBibtexDialog::browseBibPressed()
 {
-	string const file = form_->controller().browseBib("");
+	string const file = trim(form_->controller().browseBib(""));
 
 	if (!file.empty()) {
 		string const f = ChangeExtension(file, "");
@@ -102,16 +139,18 @@ void QBibtexDialog::browseBibPressed()
 	}
 }
 
+
 void QBibtexDialog::addPressed()
 {
 	add_->exec();
+	add_bc_.valid(false);
 }
 
 
 void QBibtexDialog::addDatabase()
 {
 	int const sel = add_->bibLB->currentItem();
-	QString const file = add_->bibED->text();
+	QString const file = trim(add_->bibED->text());
 
 	if (sel < 0 && file.isNull())
 		return;
diff --git a/src/frontends/qt2/QBibtexDialog.h b/src/frontends/qt2/QBibtexDialog.h
index fa6adc7f1d..f1ed4e563a 100644
--- a/src/frontends/qt2/QBibtexDialog.h
+++ b/src/frontends/qt2/QBibtexDialog.h
@@ -13,6 +13,7 @@
 #define QBIBTEXDIALOG_H
 
 #include "ui/QBibtexDialogBase.h"
+#include "ButtonController.h"
 
 class QBibtexAddDialogBase;
 
@@ -26,6 +27,7 @@ class QBibtexDialog : public QBibtexDialogBase {
 
 public:
 	QBibtexDialog(QBibtex * form);
+	~QBibtexDialog();
 
 	QBibtexAddDialogBase * add_;
 
@@ -38,12 +40,14 @@ protected slots:
 	virtual void deletePressed();
 	virtual void databaseChanged();
 	virtual void availableChanged();
+	void bibEDChanged();
 
 protected:
 	virtual void closeEvent(QCloseEvent * e);
 
 private:
 	QBibtex * form_;
+	ButtonController add_bc_;
 };
 
 } // namespace frontend
diff --git a/src/frontends/qt2/QExternal.C b/src/frontends/qt2/QExternal.C
index 47f232b467..829d76612f 100644
--- a/src/frontends/qt2/QExternal.C
+++ b/src/frontends/qt2/QExternal.C
@@ -31,6 +31,7 @@
 #include "checkedwidgets.h"
 #include "lengthcombo.h"
 #include "qt_helpers.h"
+#include "validators.h"
 
 #include <qlineedit.h>
 #include <qpushbutton.h>
@@ -320,6 +321,7 @@ void QExternal::build_dialog()
 	addCheckedLineEdit(bcview(), dialog_->ybED, dialog_->lbLA);
 	addCheckedLineEdit(bcview(), dialog_->xrED, dialog_->rtLA);
 	addCheckedLineEdit(bcview(), dialog_->ytED, dialog_->rtLA);
+	addCheckedLineEdit(bcview(), dialog_->fileED, dialog_->fileLA);
 
 	std::vector<string> templates(controller().getTemplates());
 
@@ -343,6 +345,10 @@ void QExternal::build_dialog()
 
 void QExternal::update_contents()
 {
+	PathValidator * path_validator = getPathValidator(dialog_->fileED);
+	if (path_validator)
+		path_validator->setChecker(kernel().docType(), lyxrc);
+
 	dialog_->tab->setCurrentPage(0);
 	InsetExternalParams const & params = controller().params();
 
diff --git a/src/frontends/qt2/QExternalDialog.C b/src/frontends/qt2/QExternalDialog.C
index c951728856..c5045f684b 100644
--- a/src/frontends/qt2/QExternalDialog.C
+++ b/src/frontends/qt2/QExternalDialog.C
@@ -68,6 +68,8 @@ QExternalDialog::QExternalDialog(QExternal * form)
 
 	widthED->setValidator(unsignedLengthValidator(widthED));
 	heightED->setValidator(unsignedLengthValidator(heightED));
+
+	fileED->setValidator(new PathValidator(true, fileED));
 }
 
 
diff --git a/src/frontends/qt2/QGraphics.C b/src/frontends/qt2/QGraphics.C
index dc7a68ea8b..10c182fcaf 100644
--- a/src/frontends/qt2/QGraphics.C
+++ b/src/frontends/qt2/QGraphics.C
@@ -19,6 +19,7 @@
 #include "QGraphicsDialog.h"
 #include "Qt2BC.h"
 #include "qt_helpers.h"
+#include "validators.h"
 
 #include "lengthcommon.h"
 #include "lyxrc.h"
@@ -114,6 +115,7 @@ void QGraphics::build_dialog()
 	addCheckedLineEdit(bcview(), dialog_->lbY, dialog_->yL);
 	addCheckedLineEdit(bcview(), dialog_->rtX, dialog_->xL_2);
 	addCheckedLineEdit(bcview(), dialog_->rtY, dialog_->yL_2);
+	addCheckedLineEdit(bcview(), dialog_->filename, dialog_->filenameL);
 }
 
 
@@ -131,6 +133,10 @@ int getItemNo(vector<string> v, string const & s) {
 
 void QGraphics::update_contents()
 {
+	PathValidator * path_validator = getPathValidator(dialog_->filename);
+	if (path_validator)
+		path_validator->setChecker(kernel().docType(), lyxrc);
+
 	// clear and fill in the comboboxes
 	vector<string> const bb_units = lyx::frontend::getBBUnits();
 	dialog_->lbXunit->clear();
diff --git a/src/frontends/qt2/QGraphicsDialog.C b/src/frontends/qt2/QGraphicsDialog.C
index efc2c99d33..e4361c10cf 100644
--- a/src/frontends/qt2/QGraphicsDialog.C
+++ b/src/frontends/qt2/QGraphicsDialog.C
@@ -58,6 +58,8 @@ QGraphicsDialog::QGraphicsDialog(QGraphics * form)
 	displayscale->setValidator(new QIntValidator(displayscale));
 	height->setValidator(unsignedLengthValidator(height));
 	width->setValidator(unsignedLengthValidator(width));
+
+	filename->setValidator(new PathValidator(true, filename));
 }
 
 
diff --git a/src/frontends/qt2/QInclude.C b/src/frontends/qt2/QInclude.C
index da4b2f03d5..df6ac70f87 100644
--- a/src/frontends/qt2/QInclude.C
+++ b/src/frontends/qt2/QInclude.C
@@ -12,8 +12,13 @@
 
 #include "QIncludeDialog.h"
 #include "QInclude.h"
+
+#include "checkedwidgets.h"
 #include "Qt2BC.h"
 #include "qt_helpers.h"
+#include "validators.h"
+
+#include "lyxrc.h"
 
 #include "controllers/ControlInclude.h"
 
@@ -45,11 +50,17 @@ void QInclude::build_dialog()
 	bcview().addReadOnly(dialog_->browsePB);
 	bcview().addReadOnly(dialog_->visiblespaceCB);
 	bcview().addReadOnly(dialog_->typeCO);
+
+	addCheckedLineEdit(bcview(), dialog_->filenameED, dialog_->filenameLA);
 }
 
 
 void QInclude::update_contents()
 {
+	PathValidator * path_validator = getPathValidator(dialog_->filenameED);
+	if (path_validator)
+		path_validator->setChecker(kernel().docType(), lyxrc);
+
 	InsetCommandParams const & params = controller().params();
 
 	dialog_->filenameED->setText(toqstr(params.getContents()));
diff --git a/src/frontends/qt2/QIncludeDialog.C b/src/frontends/qt2/QIncludeDialog.C
index 5e998a76b3..15f207f5fe 100644
--- a/src/frontends/qt2/QIncludeDialog.C
+++ b/src/frontends/qt2/QIncludeDialog.C
@@ -12,6 +12,7 @@
 
 #include "QIncludeDialog.h"
 #include "QInclude.h"
+#include "validators.h"
 
 #include <qpushbutton.h>
 #include <qcheckbox.h>
@@ -29,6 +30,8 @@ QIncludeDialog::QIncludeDialog(QInclude * form)
 		form, SLOT(slotOK()));
 	connect(closePB, SIGNAL(clicked()),
 		form, SLOT(slotClose()));
+
+	filenameED->setValidator(new PathValidator(true, filenameED));
 }
 
 
diff --git a/src/frontends/xforms/ChangeLog b/src/frontends/xforms/ChangeLog
index d7e30d1ac9..ffaa2a1894 100644
--- a/src/frontends/xforms/ChangeLog
+++ b/src/frontends/xforms/ChangeLog
@@ -1,3 +1,13 @@
+2005-05-13  Angus Leeming  <leeming@lyx.org>
+
+	* checkedwidgets.[Ch] (CheckedPath): new class that determines
+	whether the input file name is valid or not.
+
+	* FormExternal.[Ch]:
+	* FormGraphics.[Ch]:
+	* FormInclude.[Ch]: use the new CheckedPath to control the
+	activation state of the "OK", "Apply" buttons.
+
 2005-05-09  Lars Gullik Bjønnes  <larsbj@gullik.net>
 
 	* forms/Makefile.am: add a distclean-local target to remove
@@ -12,8 +22,8 @@
 2005-05-04  Michael Schmitt  <michael.schmitt@teststep.org>
 
 	* forms/form_preferences.fd: fix capitalization.
-	* Form*.C: Change dialog titles - harmonize with Qt frontend and 
-	menu entries; fix capitalization; change "citation reference" 
+	* Form*.C: Change dialog titles - harmonize with Qt frontend and
+	menu entries; fix capitalization; change "citation reference"
 	to "citation".
 	* FormTexinfo.C: correct tooltip.
 
diff --git a/src/frontends/xforms/FormExternal.C b/src/frontends/xforms/FormExternal.C
index 7bffb9c475..5d15458775 100644
--- a/src/frontends/xforms/FormExternal.C
+++ b/src/frontends/xforms/FormExternal.C
@@ -319,7 +319,8 @@ void getExtra(external::ExtraData & data,
 typedef FormController<ControlExternal, FormView<FD_external> > base_class;
 
 FormExternal::FormExternal(Dialog & parent)
-	: base_class(parent, _("External Material"))
+	: base_class(parent, _("External Material")),
+	  file_checker_(0)
 {}
 
 
@@ -366,6 +367,8 @@ void FormExternal::build()
 	bcview().addReadOnly(options_->choice_option);
 	bcview().addReadOnly(options_->input_option);
 
+	file_checker_ = &addCheckedPath(bcview(), true, file_->input_file);
+
 	// initial setting
 //	addCheckedPositiveFloat(bcview(), scale_->input_width);
 	// As I haven't written addCheckedPositiveFloat, we default to
@@ -464,6 +467,8 @@ void FormExternal::build()
 
 void FormExternal::update()
 {
+	file_checker_->setChecker(kernel().docType(), lyxrc);
+
 	fl_set_folder_bynumber(dialog_->tabfolder, 1);
 	InsetExternalParams const & params = controller().params();
 
diff --git a/src/frontends/xforms/FormExternal.h b/src/frontends/xforms/FormExternal.h
index f48c160be8..6eb63e400d 100644
--- a/src/frontends/xforms/FormExternal.h
+++ b/src/frontends/xforms/FormExternal.h
@@ -20,6 +20,7 @@
 namespace lyx {
 namespace frontend {
 
+class CheckedPath;
 class ControlExternal;
 struct FD_external;
 struct FD_external_file;
@@ -67,6 +68,9 @@ private:
 	void updateComboChange();
 	void widthUnitChanged();
 
+	// Accessor to checker owned by the button controller.
+	CheckedPath * file_checker_;
+
 	MapType extra_;
 
 	TabMap tabmap_;
diff --git a/src/frontends/xforms/FormGraphics.C b/src/frontends/xforms/FormGraphics.C
index d794ac0f42..a72e52d05c 100644
--- a/src/frontends/xforms/FormGraphics.C
+++ b/src/frontends/xforms/FormGraphics.C
@@ -75,7 +75,8 @@ bool const scalableTabfolders = true;
 typedef FormController<ControlGraphics, FormView<FD_graphics> > base_class;
 
 FormGraphics::FormGraphics(Dialog & parent)
-	: base_class(parent, _("Graphics"), scalableTabfolders)
+	: base_class(parent, _("Graphics"), scalableTabfolders),
+	  file_checker_(0)
 {}
 
 
@@ -110,6 +111,8 @@ void FormGraphics::build()
 	bcview().addReadOnly(file_->check_draft);
 	bcview().addReadOnly(file_->check_nounzip);
 
+	file_checker_ = &addCheckedPath(bcview(), true, file_->input_filename);
+
 	// Check validity of "length + unit" input.
 	addCheckedGlueLength(bcview(), file_->input_width);
 	addCheckedGlueLength(bcview(), file_->input_height);
@@ -431,7 +434,10 @@ void FormGraphics::apply()
 }
 
 
-void FormGraphics::update() {
+void FormGraphics::update()
+{
+	file_checker_->setChecker(kernel().docType(), lyxrc);
+
 	// Update dialog with details from inset
 	InsetGraphicsParams & igp = controller().params();
 
diff --git a/src/frontends/xforms/FormGraphics.h b/src/frontends/xforms/FormGraphics.h
index 85ee23a743..97364f3472 100644
--- a/src/frontends/xforms/FormGraphics.h
+++ b/src/frontends/xforms/FormGraphics.h
@@ -20,6 +20,7 @@
 namespace lyx {
 namespace frontend {
 
+class CheckedPath;
 class ControlGraphics;
 struct FD_graphics;
 struct FD_graphics_file;
@@ -49,6 +50,9 @@ private:
 	/// Filter the inputs on callback from xforms
 	virtual ButtonPolicy::SMInput input(FL_OBJECT *, long);
 
+	// Accessor to checker owned by the button controller.
+	CheckedPath * file_checker_;
+
 	/// Real GUI implementation.
 	boost::scoped_ptr<FD_graphics_file> file_;
 	///
diff --git a/src/frontends/xforms/FormInclude.C b/src/frontends/xforms/FormInclude.C
index 57bbb468e5..632af3beb8 100644
--- a/src/frontends/xforms/FormInclude.C
+++ b/src/frontends/xforms/FormInclude.C
@@ -16,10 +16,13 @@
 #include "ControlInclude.h"
 #include "forms/form_include.h"
 
+#include "checkedwidgets.h"
 #include "Tooltips.h"
 #include "xforms_helpers.h" // setEnabled
 #include "xformsBC.h"
 
+#include "lyxrc.h"
+
 #include "support/lstrings.h" // strip
 
 #include "lyx_forms.h"
@@ -35,7 +38,8 @@ namespace frontend {
 typedef FormController<ControlInclude, FormView<FD_include> > base_class;
 
 FormInclude::FormInclude(Dialog & parent)
-	: base_class(parent, _("Child Document"))
+	: base_class(parent, _("Child Document")),
+	  file_checker_(0)
 {}
 
 
@@ -58,6 +62,8 @@ void FormInclude::build()
 	bcview().addReadOnly(dialog_->radio_useinclude);
 	bcview().addReadOnly(dialog_->radio_verbatim);
 
+	file_checker_ = &addCheckedPath(bcview(), true, dialog_->input_filename);
+
 	type_.init(dialog_->radio_useinput,   ControlInclude::INPUT);
 	type_.init(dialog_->radio_useinclude, ControlInclude::INCLUDE);
 	type_.init(dialog_->radio_verbatim,   ControlInclude::VERBATIM);
@@ -84,6 +90,8 @@ void FormInclude::build()
 
 void FormInclude::update()
 {
+	file_checker_->setChecker(kernel().docType(), lyxrc);
+
 	string const filename = controller().params().getContents();
 	string const cmdname = controller().params().getCmdName();
 	bool const preview = static_cast<bool>((controller().params().preview()));
diff --git a/src/frontends/xforms/FormInclude.h b/src/frontends/xforms/FormInclude.h
index 5bd8464335..2846e3dd90 100644
--- a/src/frontends/xforms/FormInclude.h
+++ b/src/frontends/xforms/FormInclude.h
@@ -19,6 +19,7 @@
 namespace lyx {
 namespace frontend {
 
+class CheckedPath;
 class ControlInclude;
 struct FD_include;
 
@@ -39,6 +40,9 @@ private:
 	/// Filter the inputs on callback from xforms
 	virtual ButtonPolicy::SMInput input(FL_OBJECT *, long);
 
+	// Accessor to checker owned by the button controller.
+	CheckedPath * file_checker_;
+
 	/// include type
 	RadioButtonGroup type_;
 };
diff --git a/src/frontends/xforms/checkedwidgets.C b/src/frontends/xforms/checkedwidgets.C
index 532823e34f..9ea5dbf0e1 100644
--- a/src/frontends/xforms/checkedwidgets.C
+++ b/src/frontends/xforms/checkedwidgets.C
@@ -13,32 +13,53 @@
 
 #include "checkedwidgets.h"
 #include "xforms_helpers.h"
+
+#include "gettext.h"
 #include "lyxgluelength.h"
+#include "lyxrc.h"
+
+#include "frontends/Alert.h"
+#include "frontends/controllers/Kernel.h"
 
 #include "support/lstrings.h"
 
 #include "lyx_forms.h"
 
+#include <sstream>
+
+
+using lyx::support::isStrDbl;
 using std::string;
 
 namespace lyx {
-
-using support::isStrDbl;
-
 namespace frontend {
 
 
-void addCheckedLyXLength(BCView & bcview,
-			 FL_OBJECT * input, FL_OBJECT * label)
+CheckedLyXLength &
+addCheckedLyXLength(BCView & bcview, FL_OBJECT * input, FL_OBJECT * label)
 {
-	bcview.addCheckedWidget(new CheckedLyXLength(input, label));
+	CheckedLyXLength * cw(new CheckedLyXLength(input, label));
+	bcview.addCheckedWidget(cw);
+	return *cw;
 }
 
 
-void addCheckedGlueLength(BCView & bcview,
-			  FL_OBJECT * input, FL_OBJECT * label)
+CheckedGlueLength &
+addCheckedGlueLength(BCView & bcview, FL_OBJECT * input, FL_OBJECT * label)
 {
-	bcview.addCheckedWidget(new CheckedGlueLength(input, label));
+	CheckedGlueLength * cw(new CheckedGlueLength(input, label));
+	bcview.addCheckedWidget(cw);
+	return *cw;
+}
+
+
+CheckedPath &
+addCheckedPath(BCView & bcview, bool acceptable_if_empty,
+	       FL_OBJECT * input, FL_OBJECT * label)
+{
+	CheckedPath * cw(new CheckedPath(acceptable_if_empty, input, label));
+	bcview.addCheckedWidget(cw);
+	return *cw;
 }
 
 
@@ -107,5 +128,87 @@ bool CheckedGlueLength::check() const
 	return valid;
 }
 
+
+CheckedPath::CheckedPath(bool acceptable_if_empty,
+			 FL_OBJECT * input, FL_OBJECT * label)
+	: input_(input), label_(label ? label : input),
+	  acceptable_if_empty_(acceptable_if_empty),
+	  latex_doc_(false),
+	  tex_allows_spaces_(false)
+{}
+
+
+void CheckedPath::setChecker(lyx::frontend::KernelDocType const & type,
+			     LyXRC const & lyxrc)
+{
+	latex_doc_ = type == lyx::frontend::Kernel::LATEX;
+	tex_allows_spaces_ = lyxrc.tex_allows_spaces;
+}
+
+
+namespace {
+
+string const printable_list(string const & invalid_chars)
+{
+	std::ostringstream ss;
+	string::const_iterator const begin = invalid_chars.begin();
+	string::const_iterator const end = invalid_chars.end();
+	string::const_iterator it = begin;
+
+	for (; it != end; ++it) {
+		if (it != begin)
+			ss << ", ";
+		if (*it == ' ')
+			ss << _("space");
+		else
+			ss << *it;
+	}
+
+	return ss.str();
+}
+
+} // namespace anon
+
+
+bool CheckedPath::check() const
+{
+	if (!latex_doc_) {
+		setWidget(true, input_, label_);
+		return true;
+	}
+
+	if (!isActive(input_)) {
+		setWidget(true, input_, label_);
+		return true;
+	}
+
+	string const text = getString(input_);
+	if (text.empty()) {
+		setWidget(acceptable_if_empty_, input_, label_);
+		return acceptable_if_empty_;
+	}
+
+	string invalid_chars("#$%{}()[]:\"^");
+	if (!tex_allows_spaces_)
+		invalid_chars += ' ';
+
+	bool valid = true;
+	if (text.find_first_of(invalid_chars) != string::npos) {
+
+		static int counter = 0;
+		if (counter == 0) {
+			Alert::error(_("Invalid filename"),
+				     _("LyX does not provide LateX support for file names containing any of these characters:\n") +
+				     printable_list(invalid_chars));
+		}
+		++counter;
+		valid = false;
+	}
+
+	// set the color of label and input widget
+	setWidget(valid, input_, label_);
+	return valid;
+}
+
 } // namespace frontend
 } // namespace lyx
diff --git a/src/frontends/xforms/checkedwidgets.h b/src/frontends/xforms/checkedwidgets.h
index 1088bbcaa9..27885a1b01 100644
--- a/src/frontends/xforms/checkedwidgets.h
+++ b/src/frontends/xforms/checkedwidgets.h
@@ -18,11 +18,22 @@
 namespace lyx {
 namespace frontend {
 
-void addCheckedLyXLength(BCView & bcview,
-			 FL_OBJECT * input, FL_OBJECT * label = 0);
+class CheckedLyXLength;
+class CheckedGlueLength;
+class CheckedPath;
+
+
+//
+CheckedLyXLength &
+addCheckedLyXLength(BCView & bcview, FL_OBJECT * input, FL_OBJECT * label = 0);
+
+CheckedGlueLength &
+addCheckedGlueLength(BCView & bcview, FL_OBJECT * input, FL_OBJECT * label = 0);
+
+CheckedPath &
+addCheckedPath(BCView & bcview, bool acceptable_if_empty,
+	       FL_OBJECT * input, FL_OBJECT * label = 0);
 
-void addCheckedGlueLength(BCView & bcview,
-			  FL_OBJECT * input, FL_OBJECT * label = 0);
 
 class CheckedLyXLength : public CheckedWidget {
 public:
@@ -62,4 +73,49 @@ private:
 } // namespace frontend
 } // namespace lyx
 
+
+// Forward declarations
+class LyXRC;
+
+namespace lyx {
+namespace frontend {
+
+class KernelDocType;
+
+
+class CheckedPath : public CheckedWidget {
+public:
+	/** The label widget's label will be turned red if input
+	 *  does not make a valid file path.
+	 *  If label == 0, then the label of input will be used.
+	 *  If @c acceptable_if_empty is @c true then an empty path
+	 *  is regarded as acceptable.
+	 */
+	CheckedPath(bool acceptable_if_empty,
+		    FL_OBJECT * input, FL_OBJECT * label = 0);
+
+	/** Define now to perform the check.
+	 *  @param doc_type checks are activated only for @c LATEX docs.
+	 *  @param lyxrc contains a @c tex_allows_spaces member that
+	 *  is used to define what is legal.
+	 */
+	void setChecker(lyx::frontend::KernelDocType const & doc_type,
+			LyXRC const & lyxrc);
+
+private:
+	///
+	virtual bool check() const;
+
+	///
+	FL_OBJECT * input_;
+	FL_OBJECT * label_;
+
+	bool acceptable_if_empty_;
+	bool latex_doc_;
+	bool tex_allows_spaces_;
+};
+
+} // namespace frontend
+} // namespace lyx
+
 #endif // CHECKEDWIDGETS_H