diff --git a/gcc/ada/libgnarl/s-taprop__posix.adb b/gcc/ada/libgnarl/s-taprop__posix.adb
index 3d76679ad4a..5f6a4d69c91 100644
--- a/gcc/ada/libgnarl/s-taprop__posix.adb
+++ b/gcc/ada/libgnarl/s-taprop__posix.adb
@@ -294,7 +294,7 @@ package body System.Task_Primitives.Operations is
          Res :=
            mprotect
              (Stack_Base - (Stack_Base mod Page_Size) + Page_Size,
-              size_t (Page_Size),
+              Interfaces.C.size_t (Page_Size),
               prot => (if On then PROT_ON else PROT_OFF));
          pragma Assert (Res = 0);
       end if;