diff --git a/src/Base/UnitsApi.cpp b/src/Base/UnitsApi.cpp
index 7a4bc773c2..87b9208d38 100644
--- a/src/Base/UnitsApi.cpp
+++ b/src/Base/UnitsApi.cpp
@@ -62,7 +62,7 @@ using namespace Base;
 double UnitsApi::defaultFactor = 1.0;
 
 UnitsSchema  *UnitsApi::UserPrefSystem = new UnitsSchemaInternal();
-UnitSystem    UnitsApi::actSystem = SI1;
+UnitSystem    UnitsApi::actSystem = UnitSystem::SI1;
 
 //double   UnitsApi::UserPrefFactor [50];
 //QString  UnitsApi::UserPrefUnit   [50];
@@ -83,21 +83,21 @@ UnitsApi::~UnitsApi()
 const char* UnitsApi::getDescription(UnitSystem system)
 {
     switch (system) {
-    case SI1:
+    case UnitSystem::SI1:
         return "Standard (mm/kg/s/degree)";
-    case SI2:
+    case UnitSystem::SI2:
         return "MKS (m/kg/s/degree)";
-    case Imperial1:
+    case UnitSystem::Imperial1:
         return "US customary (in/lb)";
-    case ImperialDecimal:
+    case UnitSystem::ImperialDecimal:
         return "Imperial decimal (in/lb)";
-    case Centimeters:
+    case UnitSystem::Centimeters:
         return "Building Euro (cm/m²/m³)";
-    case ImperialBuilding:
+    case UnitSystem::ImperialBuilding:
         return "Building US (ft-in/sqft/cuft)";
-    case MmMin:
+    case UnitSystem::MmMin:
         return "Metric small parts & CNC(mm, mm/min)";
-    case ImperialCivil:
+    case UnitSystem::ImperialCivil:
         return "Imperial for Civil Eng (ft, ft/sec)";
     default:
         return "Unknown schema";
@@ -107,21 +107,21 @@ const char* UnitsApi::getDescription(UnitSystem system)
 UnitsSchema* UnitsApi::createSchema(UnitSystem s)
 {
     switch (s) {
-    case SI1:
+    case UnitSystem::SI1:
         return new UnitsSchemaInternal();
-    case SI2:
+    case UnitSystem::SI2:
         return new UnitsSchemaMKS();
-    case Imperial1:
+    case UnitSystem::Imperial1:
         return new UnitsSchemaImperial1();
-    case ImperialDecimal:
+    case UnitSystem::ImperialDecimal:
         return new UnitsSchemaImperialDecimal();
-    case Centimeters:
+    case UnitSystem::Centimeters:
         return new UnitsSchemaCentimeters();
-    case ImperialBuilding:
+    case UnitSystem::ImperialBuilding:
         return new UnitsSchemaImperialBuilding();
-    case MmMin:
+    case UnitSystem::MmMin:
         return new UnitsSchemaMmMin();
-    case ImperialCivil:
+    case UnitSystem::ImperialCivil:
         return new UnitsSchemaImperialCivil();
     default:
         break;
@@ -144,7 +144,7 @@ void UnitsApi::setSchema(UnitSystem s)
     // for wrong value fall back to standard schema
     if (!UserPrefSystem) {
         UserPrefSystem = new UnitsSchemaInternal();
-        actSystem = SI1;
+        actSystem = UnitSystem::SI1;
     }
 
     UserPrefSystem->setSchemaUnits(); // if necessary a unit schema can change the constants in Quantity (e.g. mi=1.8km rather then 1.6km).
diff --git a/src/Base/UnitsApiPy.cpp b/src/Base/UnitsApiPy.cpp
index 8aaa34b718..47ca106bc2 100644
--- a/src/Base/UnitsApiPy.cpp
+++ b/src/Base/UnitsApiPy.cpp
@@ -169,7 +169,7 @@ PyObject* UnitsApi::sParseQuantity(PyObject * /*self*/, PyObject *args)
 PyObject* UnitsApi::sListSchemas(PyObject * /*self*/, PyObject *args)
 {
     if (PyArg_ParseTuple(args, "")) {
-        int num = NumUnitSystemTypes;
+        int num = static_cast<int>(UnitSystem::NumUnitSystemTypes);
         Py::Tuple tuple(num);
         for (int i=0; i<num; i++) {
             tuple.setItem(i, Py::String(UnitsApi::getDescription(static_cast<UnitSystem>(i))));
@@ -181,7 +181,7 @@ PyObject* UnitsApi::sListSchemas(PyObject * /*self*/, PyObject *args)
     PyErr_Clear();
     int index;
     if (PyArg_ParseTuple(args, "i", &index)) {
-        int num = NumUnitSystemTypes;
+        int num = static_cast<int>(UnitSystem::NumUnitSystemTypes);
         if (index < 0 || index >= num) {
             PyErr_SetString(PyExc_ValueError, "invalid schema value");
             return 0;
@@ -207,7 +207,7 @@ PyObject* UnitsApi::sSetSchema(PyObject * /*self*/, PyObject *args)
     PyErr_Clear();
     int index;
     if (PyArg_ParseTuple(args, "i", &index)) {
-        int num = NumUnitSystemTypes;
+        int num = static_cast<int>(UnitSystem::NumUnitSystemTypes);
         if (index < 0 || index >= num) {
             PyErr_SetString(PyExc_ValueError, "invalid schema value");
             return 0;
diff --git a/src/Base/UnitsSchema.h b/src/Base/UnitsSchema.h
index c5e5bb3c70..a10bd907d3 100644
--- a/src/Base/UnitsSchema.h
+++ b/src/Base/UnitsSchema.h
@@ -33,7 +33,7 @@
 namespace Base {
 
 /** Units systems */
-enum UnitSystem {
+enum class UnitSystem {
     SI1 = 0 , /** internal (mm,kg,s) SI system (http://en.wikipedia.org/wiki/International_System_of_Units) */
     SI2 = 1 , /** MKS (m,kg,s) SI system */
     Imperial1 = 2, /** the Imperial system (http://en.wikipedia.org/wiki/Imperial_units) */
diff --git a/src/Gui/DlgSettingsUnitsImp.cpp b/src/Gui/DlgSettingsUnitsImp.cpp
index 171f0f0a09..70df3266d4 100644
--- a/src/Gui/DlgSettingsUnitsImp.cpp
+++ b/src/Gui/DlgSettingsUnitsImp.cpp
@@ -57,7 +57,7 @@ DlgSettingsUnitsImp::DlgSettingsUnitsImp(QWidget* parent)
     ui->tableWidget->setVisible(false);
     //
     // Enable/disable the fractional inch option depending on system
-    if( UnitsApi::getSchema() == ImperialBuilding )
+    if( UnitsApi::getSchema() == UnitSystem::ImperialBuilding )
     {
         ui->comboBox_FracInch->setEnabled(true);
     }
@@ -82,7 +82,7 @@ void DlgSettingsUnitsImp::on_comboBox_ViewSystem_currentIndexChanged(int index)
         return; // happens when clearing the combo box in retranslateUi()
 
     // Enable/disable the fractional inch option depending on system
-    if( (UnitSystem)index == ImperialBuilding )
+    if( (UnitSystem)index == UnitSystem::ImperialBuilding )
     {
         ui->comboBox_FracInch->setEnabled(true);
     }
diff --git a/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp b/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp
index e7b54db4ba..c7c438d1b9 100644
--- a/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp
+++ b/src/Mod/Sketcher/Gui/ViewProviderSketch.cpp
@@ -2894,20 +2894,20 @@ QString ViewProviderSketch::getPresentationString(const Constraint *constraint)
         // If this is a supported unit system then define what the base unit is.
         switch (unitSys)
         {
-            case Base::SI1:
-            case Base::MmMin:
+            case Base::UnitSystem::SI1:
+            case Base::UnitSystem::MmMin:
                 baseUnitStr = QString::fromLatin1("mm");
                 break;
 
-            case Base::SI2:
+            case Base::UnitSystem::SI2:
                 baseUnitStr = QString::fromLatin1("m");
                 break;
 
-            case Base::ImperialDecimal:
+            case Base::UnitSystem::ImperialDecimal:
                 baseUnitStr = QString::fromLatin1("in");
                 break;
 
-            case Base::Centimeters:
+            case Base::UnitSystem::Centimeters:
                 baseUnitStr = QString::fromLatin1("cm");
                 break;