diff --git a/lib/std/crypto/ff.zig b/lib/std/crypto/ff.zig
index 4a465f433635179162db81870e7a3ec162027e4d..26e3ec82fc43e221927dd539e88c9ac5f9a1caac 100644
--- a/lib/std/crypto/ff.zig
+++ b/lib/std/crypto/ff.zig
@@ -1083,12 +1083,20 @@ pub fn Modulus(comptime max_bits: comptime_int) type {
     };
 }
 
+fn valueBarrier(x: Limb) Limb {
+    if (@inComptime() or builtin.zig_backend == .stage2_c) return x;
+    return asm (""
+        : [ret] "=r" (-> Limb),
+        : [x] "0" (x),
+    );
+}
+
 const ct = if (std.options.side_channels_mitigations == .none) ct_unprotected else ct_protected;
 
 const ct_protected = struct {
     // Returns x if on is true, otherwise y.
     fn select(on: bool, x: Limb, y: Limb) Limb {
-        const mask = @as(Limb, 0) -% @intFromBool(on);
+        const mask = valueBarrier(@as(Limb, 0) -% @intFromBool(on));
         return y ^ (mask & (y ^ x));
     }