diff --git a/run b/run
index 2839f3f..c6d5a80 100755
--- a/run
+++ b/run
@@ -933,6 +933,29 @@ step40() {
   }
 }
 
+# commit 9a09651019b24a32945f73dd7a69562f2cf31581
+# Author: Andrew Kelley <andrew@ziglang.org>
+# Date:   2023-10-04T00:58:13+03:00
+#
+#     update zig1.wasm
+#
+#     Notably, this contains bug fixes related to `@errorCast` which are
+#     required by the changes to `std.io.Reader` in this branch, and the
+#     compiler source code has a dependency on `std.io.Reader`.
+STEP41=9a09651019b24a32945f73dd7a69562f2cf31581
+STEP41_=0.11.0-761-g9a09651019
+step41() {
+  rm -fr "../zig-$STEP41_"
+  git archive --prefix=zig-$STEP41_/ $STEP41 | tar -C .. -x
+  {
+    pushd "../zig-$STEP41_"
+    cp ../zig-$STEP40_/stage1/zig1.wasm stage1/zig1.wasm
+    halfbuild 17
+    popd
+  }
+}
+
+
 
 if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
   set -xeuo pipefail
@@ -981,4 +1004,5 @@ if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
   if [[ "$step" -le 38 ]]; then step38; fi
   if [[ "$step" -le 39 ]]; then step39; fi
   if [[ "$step" -le 40 ]]; then step40; fi
+  if [[ "$step" -le 41 ]]; then step41; fi
 fi