diff --git a/src/App/Expression.cpp b/src/App/Expression.cpp
index b50a82fcd9..b8c58d6d2c 100644
--- a/src/App/Expression.cpp
+++ b/src/App/Expression.cpp
@@ -2301,12 +2301,7 @@ Py::Object FunctionExpression::evaluate(const Expression *expr, int f, const std
         _EXPR_THROW("Unknown function: " << f,expr);
     }
 
-    Quantity q(scaler * output, unit);
-    if (!q.isValid()) {
-        throw Base::ValueError("Not a number");
-    }
-
-    return Py::asObject(new QuantityPy(new Quantity(q)));
+    return Py::asObject(new QuantityPy(new Quantity(scaler * output, unit)));
 }
 
 Py::Object FunctionExpression::_getPyValue() const {
diff --git a/src/Gui/DlgExpressionInput.cpp b/src/Gui/DlgExpressionInput.cpp
index 46465ff4b7..2c64c46e6b 100644
--- a/src/Gui/DlgExpressionInput.cpp
+++ b/src/Gui/DlgExpressionInput.cpp
@@ -156,13 +156,17 @@ void DlgExpressionInput::textChanged(const QString &text)
                 Base::Quantity value = n->getQuantity();
                 QString msg = value.getUserString();
 
-                if(!impliedUnit.isEmpty()) {
+                if (!value.isValid()) {
+                    throw Base::ValueError("Not a number");
+                }
+                else if (!impliedUnit.isEmpty()) {
                     if (!value.getUnit().isEmpty() && value.getUnit() != impliedUnit)
                         throw Base::UnitsMismatchError("Unit mismatch between result and required unit");
 
                     value.setUnit(impliedUnit);
 
-                } else if (!value.getUnit().isEmpty()) {
+                }
+                else if (!value.getUnit().isEmpty()) {
                     msg += QString::fromUtf8(" (Warning: unit discarded)");
 
                     QPalette p(ui->msg->palette());