diff --git a/math/private/math_pown.f90 b/math/private/math_pown.f90
index 75a862973..d11c66992 100644
--- a/math/private/math_pown.f90
+++ b/math/private/math_pown.f90
@@ -89,7 +89,7 @@ elemental function powm1_ (x) result (powm1_x)
     real(dp), intent(in) :: x
     real(dp)             :: powm1_x
 
-    powm1_x = 1_dp / x
+    powm1_x = 1.0_dp / x
 
   end function powm1_