diff --git a/qtsingleapplication/src/qtlocalpeer.cpp b/qtsingleapplication/src/qtlocalpeer.cpp
index 7e99171..d39355b 100644
--- a/qtsingleapplication/src/qtlocalpeer.cpp
+++ b/qtsingleapplication/src/qtlocalpeer.cpp
@@ -5,7 +5,9 @@
 #include "qtlocalpeer.h"
 #include <QCoreApplication>
 #include <QDataStream>
+#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
 #include <QRegularExpression>
+#endif
 #include <QTime>
 
 #if defined(Q_OS_WIN)
@@ -42,7 +44,11 @@ QtLocalPeer::QtLocalPeer(QObject* parent, const QString &appId)
 #endif
         prefix = id.section(QLatin1Char('/'), -1);
     }
+#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
     prefix.remove(QRegularExpression("[^a-zA-Z]"));
+#else
+    prefix.remove(QRegExp("[^a-zA-Z]"));
+#endif
     prefix.truncate(6);
 
     QByteArray idc = id.toUtf8();
@@ -73,7 +79,6 @@ QtLocalPeer::QtLocalPeer(QObject* parent, const QString &appId)
 }
 
 
-
 bool QtLocalPeer::isClient()
 {
     if (lockFile.isLocked())