diff --git a/src/core/include/mp-units/framework/representation_concepts.h b/src/core/include/mp-units/framework/representation_concepts.h
index 4ddbcb88..8be28d05 100644
--- a/src/core/include/mp-units/framework/representation_concepts.h
+++ b/src/core/include/mp-units/framework/representation_concepts.h
@@ -118,12 +118,11 @@ concept ComplexRepresentation = Complex<T> && WeaklyRegular<T> && requires(T a,
   { a - b } -> Complex;
   { a* b } -> Complex;
   { a / b } -> Complex;
-  // TBD
-  // { re(a) } -> Scalar;
-  // { im(a) } -> Scalar;
-  // { mod(a) } -> Scalar;
-  // { arg(a) } -> Scalar;
-  // { conj(a) } -> Complex;
+  { real(a) } -> Scalar;
+  { imag(a) } -> Scalar;
+  { abs(a) } -> Scalar;
+  { arg(a) } -> Scalar;
+  { conj(a) } -> Complex;
 };
 
 // TODO how to check for a complex(Scalar, Scalar) -> Complex?