diff --git a/build.sh b/build.sh
index ed5f9b99..9cb07950 100755
--- a/build.sh
+++ b/build.sh
@@ -102,8 +102,17 @@ echo "========================================="
 make clean >/dev/null 2>&1 || true
 
 # Phase 7 + Pool TLS defaults (pinned) + user extras
-# Default: Pool TLSはOFF（必要時のみ明示ON）。短時間ベンチでのmutexとpage faultコストを避ける。
-POOL_TLS_PHASE1_DEFAULT=${POOL_TLS_PHASE1:-0}
+# Default: Target-specific Pool TLS settings
+# - Mid-Large targets (8-34KB workloads) → Pool TLS ON (critical for performance)
+# - Tiny targets (≤1KB workloads) → Pool TLS OFF (avoid TLS overhead for short benchmarks)
+case "${TARGET}" in
+  bench_mid_large_mt_hakmem|bench_pool_tls_hakmem|bench_mid_large_mt_system|bench_pool_tls_system)
+    POOL_TLS_PHASE1_DEFAULT=${POOL_TLS_PHASE1:-1}  # ON for Mid-Large workloads
+    ;;
+  *)
+    POOL_TLS_PHASE1_DEFAULT=${POOL_TLS_PHASE1:-0}  # OFF for Tiny-focused benchmarks
+    ;;
+esac
 POOL_TLS_PREWARM_DEFAULT=${POOL_TLS_PREWARM:-0}
 POOL_TLS_BIND_BOX_DEFAULT=${POOL_TLS_BIND_BOX:-0}
 DISABLE_MINCORE_DEFAULT=${DISABLE_MINCORE:-0}