diff --git a/src/OpenFOAM/primitives/SphericalTensor/Identity.H b/src/OpenFOAM/primitives/SphericalTensor/Identity.H
index 0d645d8b91..aac5313532 100644
--- a/src/OpenFOAM/primitives/SphericalTensor/Identity.H
+++ b/src/OpenFOAM/primitives/SphericalTensor/Identity.H
@@ -77,13 +77,13 @@ public:
     }
 
     //- Return 1 for label
-    inline operator label() const
+    inline explicit operator label() const
     {
         return 1;
     }
 
     //- Return 1 for scalar
-    inline operator scalar() const
+    inline explicit operator scalar() const
     {
         return 1;
     }