diff --git a/.cargo/config.toml b/.cargo/config.toml
index 95c72bd7..a5aa7c9e 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -1,3 +1,12 @@
+[target.wasm32-wasip1]
+rustflags = [
+    "-C",
+    "target-feature=+atomics,+bulk-memory,+mutable-globals,+simd128",
+    "-C",
+    "link-arg=--max-memory=4294967296",
+]
+runner = "scripts/wasm-runner.sh"
+
 [target.wasm32-wasip1-threads]
 rustflags = [
     "-C",
@@ -5,4 +14,4 @@ rustflags = [
     "-C",
     "link-arg=--max-memory=4294967296",
 ]
-runner = "wasmtime --wasi threads"
+runner = "scripts/wasm-runner.sh"
diff --git a/scripts/wasm-runner.sh b/scripts/wasm-runner.sh
new file mode 100755
index 00000000..9ece7ff6
--- /dev/null
+++ b/scripts/wasm-runner.sh
@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [ -z "${WASM_HARNESS_ENV_RAYON_NUM_THREADS:-}" ]; then
+    if command -v nproc >/dev/null 2>&1; then
+        cores=$(nproc)
+    elif command -v sysctl >/dev/null 2>&1; then
+        cores=$(sysctl -n hw.ncpu)
+    else
+        cores=1
+    fi
+    export WASM_HARNESS_ENV_RAYON_NUM_THREADS=$cores
+fi
+
+exec wasm-harness "$@"