diff --git a/src/core/include/mp-units/bits/quantity_concepts.h b/src/core/include/mp-units/bits/quantity_concepts.h
index 42e5903a..e266d2ad 100644
--- a/src/core/include/mp-units/bits/quantity_concepts.h
+++ b/src/core/include/mp-units/bits/quantity_concepts.h
@@ -32,7 +32,7 @@ namespace mp_units {
 template<Reference auto R, RepresentationOf<get_quantity_spec(R).character> Rep>
 class quantity;
 
-#if MP_UNITS_COMP_CLANG < 17
+#if defined MP_UNITS_COMP_CLANG && MP_UNITS_COMP_CLANG < 17
 template<auto R, typename Rep>
 #else
 template<Reference auto R, typename Rep>
diff --git a/src/core/include/mp-units/bits/quantity_point_concepts.h b/src/core/include/mp-units/bits/quantity_point_concepts.h
index 695d9da3..ea58c49d 100644
--- a/src/core/include/mp-units/bits/quantity_point_concepts.h
+++ b/src/core/include/mp-units/bits/quantity_point_concepts.h
@@ -110,7 +110,7 @@ template<Reference auto R, PointOriginFor<get_quantity_spec(R)> auto PO,
          RepresentationOf<get_quantity_spec(R).character> Rep>
 class quantity_point;
 
-#if MP_UNITS_COMP_CLANG < 17
+#if defined MP_UNITS_COMP_CLANG && MP_UNITS_COMP_CLANG < 17
 template<auto PO, typename Q>
 #else
 template<PointOrigin auto PO, Quantity Q>
diff --git a/src/core/include/mp-units/quantity.h b/src/core/include/mp-units/quantity.h
index 6cd9a78e..14552fb7 100644
--- a/src/core/include/mp-units/quantity.h
+++ b/src/core/include/mp-units/quantity.h
@@ -325,7 +325,7 @@ public:
   }
 
 private:
-#if MP_UNITS_COMP_CLANG < 17
+#if defined MP_UNITS_COMP_CLANG && MP_UNITS_COMP_CLANG < 17
   template<auto R2, typename Rep2>
 #else
   template<Reference auto R2, typename Rep2>
@@ -439,7 +439,7 @@ template<auto R1, typename Rep1, auto R2, typename Rep2>
 }
 
 // make_quantity
-#if MP_UNITS_COMP_CLANG < 17
+#if defined MP_UNITS_COMP_CLANG && MP_UNITS_COMP_CLANG < 17
 template<auto R, typename Rep>
 #else
 template<Reference auto R, typename Rep>
diff --git a/src/core/include/mp-units/quantity_point.h b/src/core/include/mp-units/quantity_point.h
index 6deea3e0..9408b797 100644
--- a/src/core/include/mp-units/quantity_point.h
+++ b/src/core/include/mp-units/quantity_point.h
@@ -207,7 +207,7 @@ public:
   }
 
 private:
-#if MP_UNITS_COMP_CLANG < 17
+#if defined MP_UNITS_COMP_CLANG && MP_UNITS_COMP_CLANG < 17
   template<auto PO2, typename Q>
 #else
   template<PointOrigin auto PO2, Quantity Q>
@@ -360,7 +360,7 @@ template<QuantityPoint QP1, QuantityPointOf<QP1::absolute_point_origin> QP2>
 }
 
 // make_quantity_point
-#if MP_UNITS_COMP_CLANG < 17
+#if defined MP_UNITS_COMP_CLANG && MP_UNITS_COMP_CLANG < 17
 template<auto PO, typename Q>
 #else
 template<PointOrigin auto PO, Quantity Q>