diff --git a/src/runtime/Files.Mod b/src/runtime/Files.Mod
index 5ce79071..aede16c4 100644
--- a/src/runtime/Files.Mod
+++ b/src/runtime/Files.Mod
@@ -672,7 +672,15 @@ Especially Length would become fairly complex.
 
   PROCEDURE WriteSet* (VAR R: Rider; x: SET);
     VAR b: ARRAY 4 OF CHAR; i: LONGINT;
-  BEGIN i := SYSTEM.VAL(LONGINT, x);
+        y: SYSTEM.SET64;
+  BEGIN 
+    IF SIZE(SET) = SIZE(INTEGER) THEN
+      i := SYSTEM.VAL(INTEGER, x);
+    ELSE
+      y := x;
+      i := SYSTEM.VAL(LONGINT, y);
+    END;
+
     b[0] := CHR(i); b[1] := CHR(i DIV 100H); b[2] := CHR(i DIV 10000H); b[3] := CHR(i DIV 1000000H);
     WriteBytes(R, b, 4);
   END WriteSet;