diff --git a/src/third_party/fiat/p256.c b/src/third_party/fiat/p256.c
index f1d5316..2fe2f86 100644
--- a/src/third_party/fiat/p256.c
+++ b/src/third_party/fiat/p256.c
@@ -1120,7 +1120,7 @@
   limb_t yneq = fe_nz(r);
 
   if (!xneq && !yneq && z1nz && z2nz) {
-    point_double(x_out, y_out, z_out, x1, y1, z1);
+    point_double(x3, y3, z3, x1, y1, z1);
     return;
   }