diff --git a/src/BufferList.cpp b/src/BufferList.cpp
index ff99a090f3..fd3f19de77 100644
--- a/src/BufferList.cpp
+++ b/src/BufferList.cpp
@@ -251,6 +251,15 @@ void BufferList::emergencyWriteAll()
 }
 
 
+void BufferList::invalidateConverterCache() const
+{
+	BufferStorage::const_iterator it = bstore.begin();
+	BufferStorage::const_iterator const en = bstore.end();
+	for (; it != en; ++it)
+		(*it)->params().invalidateConverterCache();
+}
+
+
 bool BufferList::exists(FileName const & fname) const
 {
 	return getBuffer(fname) != 0;
diff --git a/src/BufferList.h b/src/BufferList.h
index 690bf6a4e4..d4ae186a90 100644
--- a/src/BufferList.h
+++ b/src/BufferList.h
@@ -124,6 +124,8 @@ public:
 	void emergencyWriteAll();
 	/// FIXME
 	void updateIncludedTeXfiles(std::string const &, OutputParams const &);
+	///
+	void invalidateConverterCache() const;
 	//@}
 
 private:
diff --git a/src/BufferParams.cpp b/src/BufferParams.cpp
index 3f0f44aeff..8e799353d0 100644
--- a/src/BufferParams.cpp
+++ b/src/BufferParams.cpp
@@ -354,11 +354,17 @@ public:
 	VSpace defskip;
 	PDFOptions pdfoptions;
 	LayoutFileIndex baseClass_;
+	/// Caching for exportableFormats, which seems to be slow.
+	std::vector<Format const *> exportableFormatList;
+	std::vector<Format const *> viewableFormatList;
+	bool isViewCacheValid;
+	bool isExportCacheValid;
 };
 
 
 BufferParams::Impl::Impl()
-	: defskip(VSpace::MEDSKIP), baseClass_(string(""))
+	: defskip(VSpace::MEDSKIP), baseClass_(string("")),
+	  isViewCacheValid(false), isExportCacheValid(false)
 {
 	// set initial author
 	// FIXME UNICODE
@@ -2252,6 +2258,7 @@ void BufferParams::setDocumentClass(DocumentClassConstPtr tc)
 {
 	// evil, but this function is evil
 	doc_class_ = const_pointer_cast<DocumentClass>(tc);
+	invalidateConverterCache();
 }
 
 
@@ -2310,6 +2317,7 @@ void BufferParams::makeDocumentClass(bool const clone)
 	if (!baseClass())
 		return;
 
+	invalidateConverterCache();
 	LayoutModuleList mods;
 	LayoutModuleList::iterator it = layout_modules_.begin();
 	LayoutModuleList::iterator en = layout_modules_.end();
@@ -2405,8 +2413,15 @@ bool BufferParams::isExportable(string const & format) const
 }
 
 
-vector<Format const *> BufferParams::exportableFormats(bool only_viewable) const
+vector<Format const *> const & BufferParams::exportableFormats(bool only_viewable) const
 {
+	vector<Format const *> & cached = only_viewable ?
+			pimpl_->viewableFormatList : pimpl_->exportableFormatList;
+	bool & valid = only_viewable ? 
+			pimpl_->isViewCacheValid : pimpl_->isExportCacheValid;
+	if (valid)
+		return cached;
+
 	vector<string> const backs = backends();
 	set<string> excludes;
 	if (useNonTeXFonts) {
@@ -2421,15 +2436,16 @@ vector<Format const *> BufferParams::exportableFormats(bool only_viewable) const
 			theConverters().getReachable(*it, only_viewable, false, excludes);
 		result.insert(result.end(), r.begin(), r.end());
 	}
-	return result;
+	cached = result;
+	valid = true;
+	return cached;
 }
 
 
 bool BufferParams::isExportableFormat(string const & format) const
 {
 	typedef vector<Format const *> Formats;
-	Formats formats;
-	formats = exportableFormats(true);
+	Formats const & formats = exportableFormats(true);
 	Formats::const_iterator fit = formats.begin();
 	Formats::const_iterator end = formats.end();
 	for (; fit != end ; ++fit) {
@@ -2526,7 +2542,7 @@ string BufferParams::getDefaultOutputFormat() const
 		return default_output_format;
 	if (isDocBook()
 	    || encoding().package() == Encoding::japanese) {
-		vector<Format const *> const formats = exportableFormats(true);
+		vector<Format const *> const & formats = exportableFormats(true);
 		if (formats.empty())
 			return string();
 		// return the first we find
@@ -3294,4 +3310,10 @@ vector<CitationStyle> BufferParams::citeStyles() const
 	return styles;
 }
 
+void BufferParams::invalidateConverterCache() const
+{
+	pimpl_->isExportCacheValid = false;
+	pimpl_->isViewCacheValid = false;
+}
+
 } // namespace lyx
diff --git a/src/BufferParams.h b/src/BufferParams.h
index caae01dfec..b034b8801c 100644
--- a/src/BufferParams.h
+++ b/src/BufferParams.h
@@ -181,7 +181,7 @@ public:
 	///
 	bool isExportable(std::string const & format) const;
 	///
-	std::vector<Format const *> exportableFormats(bool only_viewable) const;
+	std::vector<const Format *> const & exportableFormats(bool only_viewable) const;
 	///
 	bool isExportableFormat(std::string const & format) const;
 	/// the backends appropriate for use with this document.
@@ -504,6 +504,8 @@ public:
 	/// Return true if language could be set to lang,
 	/// otherwise return false and do not change language
 	bool setLanguage(std::string const & lang);
+	///
+	void invalidateConverterCache() const;
 
 private:
 	///
@@ -552,7 +554,7 @@ private:
 	 *  mathdots, stackrel, stmaryrd and undertilde.
 	 */
 	PackageMap use_packages;
-
+	
 	/** Use the Pimpl idiom to hide those member variables that would otherwise
 	 *  drag in other header files.
 	 */
diff --git a/src/LyXRC.cpp b/src/LyXRC.cpp
index 7696d0991f..71e3894598 100644
--- a/src/LyXRC.cpp
+++ b/src/LyXRC.cpp
@@ -18,6 +18,7 @@
 
 #include "LyXRC.h"
 
+#include "BufferList.h"
 #include "ColorSet.h"
 #include "Converter.h"
 #include "FontEnums.h"
@@ -1226,6 +1227,7 @@ LyXRC::ReturnValues LyXRC::read(Lexer & lexrc, bool check_format)
 	/// Update converters data-structures
 	theConverters().update(formats);
 	theConverters().buildGraph();
+	theBufferList().invalidateConverterCache();
 
 	return ReadOK;
 }
diff --git a/src/frontends/qt4/GuiPrefs.cpp b/src/frontends/qt4/GuiPrefs.cpp
index d9c4207c35..e5d821b601 100644
--- a/src/frontends/qt4/GuiPrefs.cpp
+++ b/src/frontends/qt4/GuiPrefs.cpp
@@ -3412,7 +3412,8 @@ void GuiPreferences::dispatchParams()
 	theConverters() = converters_;
 	theConverters().update(lyx::formats);
 	theConverters().buildGraph();
-
+	theBufferList().invalidateConverterCache();
+	
 	theMovers() = movers_;
 
 	vector<string>::const_iterator it = colors_.begin();