diff --git a/src/support/Systemcall.cpp b/src/support/Systemcall.cpp
index 5262da7a26..d339e11b80 100644
--- a/src/support/Systemcall.cpp
+++ b/src/support/Systemcall.cpp
@@ -13,14 +13,13 @@
 
 #include <config.h>
 
-#include "support/Systemcall.h"
-#include "support/SystemcallPrivate.h"
-
 #include "support/debug.h"
 #include "support/filetools.h"
 #include "support/gettext.h"
 #include "support/lstrings.h"
 #include "support/qstring_helpers.h"
+#include "support/Systemcall.h"
+#include "support/SystemcallPrivate.h"
 #include "support/os.h"
 #include "support/ProgressInterface.h"
 
@@ -164,20 +163,19 @@ namespace {
  *    "\a"   ->  "\a"
  *    "a\"b" ->  "a"""b"
  */
-QStringList const parsecmd(string const & incmd, string & infile, string & outfile,
-                           string & errfile)
+string const parsecmd(string const & incmd, string & infile, string & outfile,
+                     string & errfile)
 {
 	bool in_single_quote = false;
 	bool in_double_quote = false;
 	bool escaped = false;
 	string const python_call = os::python();
-	QStringList arguments;
 	vector<string> outcmd(4);
 	size_t start = 0;
 
-	if (prefixIs(incmd, python_call + ' ')) {
-		arguments << QString::fromLocal8Bit(trim(os::python()).c_str());
-		start = python_call.length() + 1;
+	if (prefixIs(incmd, python_call)) {
+		outcmd[0] = os::python();
+		start = python_call.length();
 	}
 
 	for (size_t i = start, o = 0; i < incmd.length(); ++i) {
@@ -196,12 +194,30 @@ QStringList const parsecmd(string const & incmd, string & infile, string & outfi
 			outcmd[o] += c;
 			continue;
 		}
-		if (c == ' ' && !(in_double_quote || escaped)) {
-			if (o == 0)
-				arguments << QString::fromLocal8Bit(trim(outcmd[o]).c_str());
-			o = 0;
+		if (c == '"') {
+			if (escaped) {
+				// Don't triple double-quotes for redirection
+				// files as these won't be parsed by QProcess
+				outcmd[o] += string(o ? "\"" : "\"\"\"");
+				escaped = false;
+			} else {
+				outcmd[o] += c;
+				in_double_quote = !in_double_quote;
+			}
+		} else if (c == '\\' && !escaped) {
+			escaped = true;
+		} else if (c == '>' && !(in_double_quote || escaped)) {
+			if (suffixIs(outcmd[o], " 2")) {
+				outcmd[o] = rtrim(outcmd[o], "2");
+				o = 2;
+			} else {
+				if (suffixIs(outcmd[o], " 1"))
+					outcmd[o] = rtrim(outcmd[o], "1");
+				o = 1;
+			}
+		} else if (c == '<' && !(in_double_quote || escaped)) {
+			o = 3;
 #if defined (USE_MACOSX_PACKAGING)
-			// FIXME!!!!
 		} else if (o == 0 && i > 4 && c == ' ' && !(in_double_quote || escaped)) {
 			// if a macOS app is detected with an additional argument
 			// use open command as prefix to get it work
@@ -216,28 +232,6 @@ QStringList const parsecmd(string const & incmd, string & infile, string & outfi
 			}
 			outcmd[o] += c;
 #endif
-		} else if (c == '"') {
-			if (escaped) {
-				outcmd[o] += c;
-				escaped = false;
-			} else
-				in_double_quote = !in_double_quote;
-		} else if (c == '\\' && !escaped) {
-			escaped = true;
-		} else if (c == '>' && o == 0 && !(in_double_quote || escaped)) {
-			if (outcmd[o] == "2") {
-				outcmd[o].clear();
-				o = 2;
-				outcmd[o].clear();
-			} else if (outcmd[o] == "1" || outcmd[o].empty()) {
-				outcmd[o].clear();
-				o = 1;
-				outcmd[o].clear();
-			}
-		} else if (c == '<' && o == 0 && outcmd[o].empty() && !(in_double_quote || escaped)) {
-				outcmd[o].clear();
-				o = 3;
-				outcmd[o].clear();
 		} else {
 			if (escaped && in_double_quote)
 				outcmd[o] += '\\';
@@ -248,7 +242,7 @@ QStringList const parsecmd(string const & incmd, string & infile, string & outfi
 	infile  = trim(outcmd[3], " \"");
 	outfile = trim(outcmd[1], " \"");
 	errfile = trim(outcmd[2], " \"");
-	return arguments;
+	return trim(outcmd[0]);
 }
 
 } // namespace
@@ -273,7 +267,8 @@ int Systemcall::startscript(Starttype how, string const & what,
 	string infile;
 	string outfile;
 	string errfile;
-	QStringList const cmd = parsecmd(what_ss, infile, outfile, errfile);
+	QString const cmd = QString::fromLocal8Bit(
+			parsecmd(what_ss, infile, outfile, errfile).c_str());
 
 	SystemcallPrivate d(infile, outfile, errfile);
 	bool do_events = process_events || how == WaitLoop;
@@ -384,21 +379,27 @@ SystemcallPrivate::SystemcallPrivate(std::string const & sf, std::string const &
 }
 
 
-void SystemcallPrivate::startProcess(string const & cmd, string const & path,
+void SystemcallPrivate::startProcess(QString const & cmd, string const & path,
                                      string const & lpath, bool detached)
 {
-	cmd_ = toqstr(cmd);
-
-	// Set the environment for LaTeX
-	QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
-	for (auto const & v : latexEnvironment(path, lpath))
-		latexenv.insert(toqstr(v.first), QString::fromLocal8Bit(v.second.c_str()));
-	process_->setProcessEnvironment(env);
-
-	// Parse the command line
-	QStringList arguments = parsecmd(cmd);
-	QString command = arguments.empty() ? QString() : arguments.takeFirst();
-
+	cmd_ = cmd;
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
+	// FIXME pass command and arguments separated in the first place
+	/* The versions of startDetached() and start() that accept a
+	 * QStringList object exist since Qt4, but it is only in Qt 5.15
+	 * that splitCommand() was introduced and the plain versions of
+	 * start/startDetached() have been deprecated.
+	 * 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.
+	*/
+	QStringList arguments = QProcess::splitCommand(toqstr(latexEnvCmdPrefix(path, lpath)) + cmd_);
+	QString command = (arguments.empty()) ? QString() : arguments.first();
+	if (arguments.size() == 1)
+		arguments.clear();
+	else if (!arguments.empty())
+		arguments.removeFirst();
+#endif
 	if (detached) {
 		state = SystemcallPrivate::Running;
 #ifdef Q_OS_WIN32
@@ -410,8 +411,11 @@ void SystemcallPrivate::startProcess(string const & cmd, string const & path,
 		if (err_file_.empty())
 			process_->setStandardErrorFile(QProcess::nullDevice());
 #endif
-
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
 		if (!QProcess::startDetached(command, arguments)) {
+#else
+		if (!QProcess::startDetached(toqstr(latexEnvCmdPrefix(path, lpath)) + cmd_)) {
+#endif
 			state = SystemcallPrivate::Error;
 			return;
 		}
@@ -419,7 +423,11 @@ void SystemcallPrivate::startProcess(string const & cmd, string const & path,
 		delete released;
 	} else if (process_) {
 		state = SystemcallPrivate::Starting;
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 15, 0))
 		process_->start(command, arguments);
+#else
+		process_->start(toqstr(latexEnvCmdPrefix(path, lpath)) + cmd_);
+#endif
 	}
 }
 
diff --git a/src/support/SystemcallPrivate.h b/src/support/SystemcallPrivate.h
index f9b27c3430..19771dfc73 100644
--- a/src/support/SystemcallPrivate.h
+++ b/src/support/SystemcallPrivate.h
@@ -44,7 +44,7 @@ public:
 	State state;
 
 	bool waitWhile(State, bool processEvents, int timeout = -1);
-	void startProcess(std::string const & cmd, std::string const & path,
+	void startProcess(QString const & cmd, std::string const & path,
 	                  std::string const & lpath, bool detach);
 
 	int exitCode();
diff --git a/src/support/filetools.cpp b/src/support/filetools.cpp
index 1bff01460d..d554f477eb 100644
--- a/src/support/filetools.cpp
+++ b/src/support/filetools.cpp
@@ -737,13 +737,12 @@ string const replaceEnvironmentPath(string const & path)
 
 
 // Return a command prefix for setting the environment of the TeX engine.
-map <string,string> latexEnvironment(string const & path, string const & lpath)
+string latexEnvCmdPrefix(string const & path, string const & lpath)
 {
-	map<string, string> env;
 	bool use_lpath = !(lpath.empty() || lpath == "." || lpath == "./");
 
 	if (path.empty() || (lyxrc.texinputs_prefix.empty() && !use_lpath))
-		return env;
+		return string();
 
 	string texinputs_prefix = lyxrc.texinputs_prefix.empty() ? string()
 		: os::latex_path_list(
@@ -767,37 +766,30 @@ map <string,string> latexEnvironment(string const & path, string const & lpath)
 			texinputs_prefix.append(sep + abslpath);
 	}
 
-	// NOTE: the dummy blank dirs are necessary to force the
-	//       QProcess parser to quote the argument (see bug 9453)
-	string const dummy = (os::shell() == os::UNIX) ? string() : (" " + sep);
-
-	env.insert({ "TEXINPUTS", "." + sep + dummy + texinputs_prefix + sep + texinputs });
-	env.insert({ "BIBINPUTS", "." + sep + dummy + allother_prefix + sep + bibinputs });
-	env.insert({ "BSTINPUTS", "." + sep + dummy + allother_prefix + sep + bstinputs });
-	env.insert({ "TEXFONTS", "." + sep + dummy + allother_prefix + sep + texfonts });
-
-	return env;
-}
-
-
-// Return a command prefix for setting the environment of the TeX engine.
-string latexEnvCmdPrefix(string const & path, string const & lpath)
-{
-	auto const env = latexEnvironment(path, lpath);
-	if (env.empty())
-		return string();
-
-	string prefix;
-	if (os::shell() == os::UNIX) {
-		prefix = "env ";
-		for (auto const & v : latexEnvironment(path, lpath))
-			prefix += v.first + "=" + v.second + " ";
-	} else {
-		prefix = "cmd /d /c ";
-		for (auto const & v : latexEnvironment(path, lpath))
-			prefix += "set \"" + v.first + "=" + v.second + "\" & ";
-	}
-	return prefix;
+	if (os::shell() == os::UNIX)
+		return "env TEXINPUTS=\"." + sep + texinputs_prefix
+		                           + sep + texinputs + "\" "
+		         + "BIBINPUTS=\"." + sep + allother_prefix
+		                           + sep + bibinputs + "\" "
+		         + "BSTINPUTS=\"." + sep + allother_prefix
+		                           + sep + bstinputs + "\" "
+		         + "TEXFONTS=\"."  + sep + allother_prefix
+		                           + sep + texfonts + "\" ";
+	else
+		// NOTE: the dummy blank dirs are necessary to force the
+		//       QProcess parser to quote the argument (see bug 9453)
+		return "cmd /d /c set \"TEXINPUTS=." + sep + " "
+		                                + sep + texinputs_prefix
+		                                + sep + texinputs + "\" & "
+		               + "set \"BIBINPUTS=." + sep + " "
+		                                + sep + allother_prefix
+		                                + sep + bibinputs + "\" & "
+		               + "set \"BSTINPUTS=." + sep + " "
+		                                + sep + allother_prefix
+		                                + sep + bstinputs + "\" & "
+		               + "set \"TEXFONTS=."  + sep + " "
+		                                + sep + allother_prefix
+		                                + sep + texfonts + "\" & ";
 }
 
 
diff --git a/src/support/filetools.h b/src/support/filetools.h
index a4ee8e3380..404dec210f 100644
--- a/src/support/filetools.h
+++ b/src/support/filetools.h
@@ -14,10 +14,9 @@
 
 #include "support/docstring.h"
 
-#include <map>
-#include <set>
-#include <string>
 #include <utility>
+#include <string>
+#include <set>
 
 namespace lyx {
 namespace support {
@@ -290,15 +289,6 @@ std::string const onlyFileName(std::string const & fname);
 */
 std::string const replaceEnvironmentPath(std::string const & path);
 
-
-/**
-   Return a map to be used to set the environment of the TeX engine
-   with respect to the paths \p path and \p lpath.
- */
-std::map <std::string, std::string>
-latexEnvironment(std::string const & path, std::string const & lpath);
-
-
 /**
    Return a string to be used as a prefix to a command for setting the
    environment of the TeX engine with respect to the paths \p path and \p lpath.