diff --git a/src/Base/UnitsSchema.h b/src/Base/UnitsSchema.h
index 2aa3b28982..bfe5fab95f 100644
--- a/src/Base/UnitsSchema.h
+++ b/src/Base/UnitsSchema.h
@@ -67,10 +67,10 @@ public:
     QString toLocale(const Base::Quantity& quant, double factor, const QString& unitString) const;
 
     //return true if this schema uses multiple units for length (ex. Ft/In)
-    virtual bool isMultiUnitLength() {return false;}
+    virtual bool isMultiUnitLength() const {return false;}
 
     //return true if this schema uses multiple units for angles (ex. DMS)
-    virtual bool isMultiUnitAngle() {return false;}
+    virtual bool isMultiUnitAngle() const {return false;}
 };
 
 
diff --git a/src/Base/UnitsSchemaImperial1.h b/src/Base/UnitsSchemaImperial1.h
index 9d9326c821..aaed330630 100644
--- a/src/Base/UnitsSchemaImperial1.h
+++ b/src/Base/UnitsSchemaImperial1.h
@@ -67,7 +67,7 @@ public:
     QString schemaTranslate(const Base::Quantity& quant, double &factor, QString &unitString) override;
 
     //return true if this schema uses multiple units for length (ex. Ft/In)
-    bool isMultiUnitLength() override {return true;}
+    bool isMultiUnitLength() const override {return true;}
 
 };
 
@@ -83,7 +83,7 @@ public:
     QString schemaTranslate(const Base::Quantity& quant, double &factor, QString &unitString) override;
 
     //return true if this schema uses multiple units for angles (ex. DMS)
-    bool isMultiUnitAngle() override {return true;}
+    bool isMultiUnitAngle() const override {return true;}
 };