diff --git a/gcc/ada/opt.ads b/gcc/ada/opt.ads
index aea52f3ad697c93d3a1d0535b68ed1b1a70c9f20..a09a1ccffa6f159809b82071f9ba881970182d23 100644
--- a/gcc/ada/opt.ads
+++ b/gcc/ada/opt.ads
@@ -127,7 +127,7 @@ package Opt is
    --  remains set to Ada_Version_Default). This is used in the rare cases
    --  (notably pragma Obsolescent) where we want the explicit version set.
 
-   Ada_Version_Runtime : Ada_Version_Type := Ada_With_All_Extensions;
+   Ada_Version_Runtime : constant Ada_Version_Type := Ada_With_All_Extensions;
    --  GNAT
    --  Ada version used to compile the runtime. Used to set Ada_Version (but
    --  not Ada_Version_Explicit) when compiling predefined or internal units.