diff --git a/src/BufferParams.cpp b/src/BufferParams.cpp
index f7516fc026..6bb90d0be0 100644
--- a/src/BufferParams.cpp
+++ b/src/BufferParams.cpp
@@ -3840,5 +3840,11 @@ string const BufferParams::bibFileEncoding(string const & file) const
 }
 
 
+BufferParams const & defaultBufferParams()
+{
+	static BufferParams default_params;
+	return default_params;
+}
+
 
 } // namespace lyx
diff --git a/src/BufferParams.h b/src/BufferParams.h
index 890d8843a7..77b4856b4d 100644
--- a/src/BufferParams.h
+++ b/src/BufferParams.h
@@ -691,6 +691,10 @@ private:
 	support::copied_ptr<Impl, MemoryTraits> pimpl_;
 };
 
+
+///
+BufferParams const & defaultBufferParams();
+
 } // namespace lyx
 
 #endif
diff --git a/src/Converter.cpp b/src/Converter.cpp
index 172b2a2091..b63f77146a 100644
--- a/src/Converter.cpp
+++ b/src/Converter.cpp
@@ -646,21 +646,24 @@ Converters::RetVal Converters::convert(Buffer const * buffer,
 				to_utf8(makeRelPath(from_utf8(outfile.absFileName()), from_utf8(path)));
 
 			string command = conv.command();
+			BufferParams const & bparams = buffer ? buffer->params() : defaultBufferParams();
 			command = subst(command, token_from, quoteName(infile2));
 			command = subst(command, token_base, quoteName(from_base));
 			command = subst(command, token_to, quoteName(outfile2));
 			command = subst(command, token_path, quoteName(onlyPath(infile.absFileName())));
 			command = subst(command, token_orig_path, quoteName(onlyPath(orig_from.absFileName())));
 			command = subst(command, token_orig_from, quoteName(onlyFileName(orig_from.absFileName())));
-			command = subst(command, token_textclass,
-			                buffer ? quoteName(buffer->params().documentClass().name())
-			                       : string());
-			command = subst(command, token_modules,
-			                buffer ? quoteName(buffer->params().getModules().asString())
-			                       : string());
-			command = subst(command, token_encoding,
-			                buffer ? quoteName(buffer->params().encoding().iconvName())
-			                       : string());
+			command = subst(command, token_textclass, quoteName(bparams.documentClass().name()));
+			string modules = bparams.getModules().asString();
+			// FIXME: remove when SystemCall uses QProcess with the list API.
+			// Currently the QProcess parser is not able to encode an
+			// empty argument as ""; work around this by passing a
+			// single comma, that will be interpreted as a list of two
+			// empty module names.
+			if (modules.empty())
+				modules = ",";
+			command = subst(command, token_modules, quoteName(modules));
+			command = subst(command, token_encoding, quoteName(bparams.encoding().iconvName()));
 			command = subst(command, token_python, os::python());
 
 			if (!conv.parselog().empty())
diff --git a/src/support/Systemcall.cpp b/src/support/Systemcall.cpp
index d339e11b80..20fe1034b9 100644
--- a/src/support/Systemcall.cpp
+++ b/src/support/Systemcall.cpp
@@ -392,6 +392,11 @@ void SystemcallPrivate::startProcess(QString const & cmd, string const & path,
 	 * The cleanest solution would be to have parsecmd() produce a
 	 * QStringList for arguments, instead of transforming the string
 	 * into something that the QProcess splitter accepts.
+	 *
+	 * Another reason for doing that is that the Qt parser ignores
+	 * empty "" arguments, which are needed in some instances (see
+	 * e.g. the work around for modules in Converter:convert. See
+	 * QTBUG-80640 for a discussion.
 	*/
 	QStringList arguments = QProcess::splitCommand(toqstr(latexEnvCmdPrefix(path, lpath)) + cmd_);
 	QString command = (arguments.empty()) ? QString() : arguments.first();
diff --git a/src/tex2lyx/tex2lyx.cpp b/src/tex2lyx/tex2lyx.cpp
index 1b11a45ba4..0d588d2838 100644
--- a/src/tex2lyx/tex2lyx.cpp
+++ b/src/tex2lyx/tex2lyx.cpp
@@ -699,8 +699,6 @@ int parse_class(string const & arg, string const &)
 
 int parse_module(string const & arg, string const &)
 {
-	if (arg.empty())
-		error_message("Missing modules string after -m switch");
 	split(arg, preloaded_modules, ',');
 	return 1;
 }
@@ -924,11 +922,12 @@ bool tex2lyx(idocstream & is, ostream & os, string const & encoding,
 
 	// Load preloaded modules.
 	// This needs to be done after the preamble is parsed, since the text
-	// class may not be known before. It neds to be done before parsing
+	// class may not be known before. It needs to be done before parsing
 	// body, since otherwise the commands/environments provided by the
 	// modules would be parsed as ERT.
+	// Empty module names are silently skipped.
 	for (auto const & module : preloaded_modules) {
-		if (!addModule(module)) {
+		if (!module.empty() && !addModule(module)) {
 			cerr << "Error: Could not load module \""
 			     << module << "\"." << endl;
 			return false;