diff --git a/src/Base/UnitsSchemaInternal.cpp b/src/Base/UnitsSchemaInternal.cpp
index c91555c846..56e961d99e 100644
--- a/src/Base/UnitsSchemaInternal.cpp
+++ b/src/Base/UnitsSchemaInternal.cpp
@@ -42,6 +42,14 @@ QString UnitsSchemaInternal::schemaTranslate(const Quantity &quant, double &fact
     double UnitValue = std::abs(quant.getValue());
     Unit unit = quant.getUnit();
 
+    // In order to get the right factor always express the target
+    // units as internal units where length is in mm and mass in kg
+    // Example:
+    // For W/mm/K we get the factor of 1000000.0 because
+    // W/mm/K = kg*m^2/s^3/mm/K
+    // = 10e6 * kg*mm^2/s^3/mm/K
+    // = 10e6 * kg*mm/s^3/K
+
     // now do special treatment on all cases seems necessary:
     if (unit == Unit::Length) {  // Length handling ============================
         if (UnitValue < 0.000000001) {// smaller then 0.001 nm -> scientific notation
@@ -108,7 +116,7 @@ QString UnitsSchemaInternal::schemaTranslate(const Quantity &quant, double &fact
     else if (unit == Unit::ThermalConductivity) {
         if (UnitValue < 1000) {
             unitString = QString::fromLatin1("W/mm/K");
-            factor = 1.0;
+            factor = 1000000.0;
         }
         else {
             unitString = QString::fromLatin1("W/m/K");
diff --git a/src/Base/UnitsSchemaMKS.cpp b/src/Base/UnitsSchemaMKS.cpp
index f4f261ac06..645bfb952e 100644
--- a/src/Base/UnitsSchemaMKS.cpp
+++ b/src/Base/UnitsSchemaMKS.cpp
@@ -131,7 +131,7 @@ QString UnitsSchemaMKS::schemaTranslate(const Quantity &quant, double &factor, Q
     else if (unit == Unit::ThermalConductivity) {
         if (UnitValue < 1000) {
             unitString = QString::fromLatin1("W/mm/K");
-            factor = 1.0;
+            factor = 1000000.0;
         }
         else {
             unitString = QString::fromLatin1("W/m/K");
diff --git a/src/Mod/Test/UnitTests.py b/src/Mod/Test/UnitTests.py
index 9b1a151b93..dab8680787 100644
--- a/src/Mod/Test/UnitTests.py
+++ b/src/Mod/Test/UnitTests.py
@@ -4,10 +4,16 @@ import FreeCAD
 import unittest
 import math
 
-
 def tu(str):
     return FreeCAD.Units.Quantity(str).Value
 
+def ts(q):
+    return q.UserString
+
+def ts2(q):
+    return FreeCAD.Units.Quantity(q.UserString).UserString
+
+
 #---------------------------------------------------------------------------
 # define the functions to test the FreeCAD UnitApi code
 #---------------------------------------------------------------------------
@@ -36,6 +42,14 @@ class UnitBasicCases(unittest.TestCase):
         #self.failUnless(compare(tu('1fo(3+7/16)in'),392.112500))thisgivesaparsersyntaxerror!!!
         self.failUnless(compare(tu('1\'(3+7/16)"'), 392.112500))
 
+    def testSelfConsistency(self):
+        qu = FreeCAD.Units.Quantity("0.23 W/m/K")
+        self.assertTrue(ts(qu), ts2(qu))
+        qu = FreeCAD.Units.Quantity("237 mm*kg/(s^3*K)")
+        self.assertTrue(ts(qu), ts2(qu))
+        qu = FreeCAD.Units.Quantity("237.000 W/mm/K")
+        self.assertTrue(ts(qu), ts2(qu))
+
     def testTrigonometric(self):
         #tu=FreeCAD.Units.translateUnit
         self.failUnless(compare(tu('sin(pi)'), math.sin(math.pi)))