diff --git a/src/gcodecommands.cpp b/src/gcodecommands.cpp
--- a/src/gcodecommands.cpp
+++ b/src/gcodecommands.cpp
@@ -509,6 +509,12 @@
 {
 
     switch (gcode) {
+    case M84: {
+        if (!value1.isEmpty()) {
+            return QStringLiteral("M84 S%1").arg(value1);
+        }
+        return QStringLiteral("M84");
+    }
     case M104: {
         if (!value2.isEmpty()) {
             return QStringLiteral("M104 P%1 S%2").arg(value1).arg(value2);
diff --git a/unittests/gcodetests.h b/unittests/gcodetests.h
--- a/unittests/gcodetests.h
+++ b/unittests/gcodetests.h
@@ -59,6 +59,7 @@
     void string_G161();
     void string_G162();
 
+    void command_M84();
     void command_M104();
     void command_M105();
     void command_M106();
diff --git a/unittests/gcodetests.cpp b/unittests/gcodetests.cpp
--- a/unittests/gcodetests.cpp
+++ b/unittests/gcodetests.cpp
@@ -183,6 +183,12 @@
     QVERIFY(GCode::toString(GCode::G162) == QObject::tr("G162: Home axis to maximum"));
 }
 
+void GCodeTests::command_M84()
+{
+    QVERIFY(GCode::toCommand(GCode::M84) == QStringLiteral("M84"));
+    QVERIFY(GCode::toCommand(GCode::M84, QStringLiteral("10")) == QStringLiteral("M84 S10"));
+}
+
 void GCodeTests::command_M104()
 {
     QVERIFY(GCode::toCommand(GCode::M104) == QStringLiteral("ERROR! M104: It's obligatory to have an argument"));