diff --git a/CHANGELOG.md b/CHANGELOG.md
index 184c9512f..ba7e89635 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@
 - Thinking: default to low for reasoning-capable models when no /think or config default is set.
 - Logging: decouple file log levels from console verbosity; verbose-only details are captured when `logging.level` is debug/trace.
 - Build: fix regex literal in tool-meta path detection (watch build error).
+- Build: require AVX2 Bun for x86_64 relay packaging (reject baseline builds).
 - Auto-reply: add run-level telemetry + typing TTL guardrails to diagnose stuck replies.
 
 ### Docs
diff --git a/scripts/package-mac-app.sh b/scripts/package-mac-app.sh
index 32825c5e9..8b3da678d 100755
--- a/scripts/package-mac-app.sh
+++ b/scripts/package-mac-app.sh
@@ -115,7 +115,15 @@ build_relay_binary() {
       echo "ERROR: Rosetta is required to build the x86_64 relay. Install Rosetta and retry." >&2
       exit 1
     fi
-    local bun_x86="${BUN_X86_64_BIN:-$HOME/.bun-x64/bin/bun}"
+    local bun_x86="${BUN_X86_64_BIN:-$HOME/.bun-x64/bun-darwin-x64/bun}"
+    if [[ ! -x "$bun_x86" ]]; then
+      bun_x86="$HOME/.bun-x64/bin/bun"
+    fi
+    if [[ "$bun_x86" == *baseline* ]]; then
+      echo "ERROR: x86_64 relay builds are locked to AVX2; baseline Bun is not allowed." >&2
+      echo "Set BUN_X86_64_BIN to a non-baseline Bun (bun-darwin-x64)." >&2
+      exit 1
+    fi
     if [[ -x "$bun_x86" ]]; then
       cmd=("$bun_x86" build "$ROOT_DIR/dist/macos/relay.js" --compile --bytecode --outfile "$out" -e electron --define "$define_arg")
     fi