diff --git a/changelog.d/8995-compiled-package-regexp.md b/changelog.d/8995-compiled-package-regexp.md
new file mode 100644
index 0000000000..e3550e89a5
--- /dev/null
+++ b/changelog.d/8995-compiled-package-regexp.md
@@ -0,0 +1,4 @@
+Compiled packages retain RegExp method behavior when they receive a regular
+expression created by application code, including on macOS allocations below
+2 TB. This covers schema-library paths such as zod regex and datetime checks
+when compiling with the full prebuilt stdlib.
diff --git a/crates/perry-runtime/src/value/addr_class.rs b/crates/perry-runtime/src/value/addr_class.rs
index 85d4f5905c..b128e48802 100644
--- a/crates/perry-runtime/src/value/addr_class.rs
+++ b/crates/perry-runtime/src/value/addr_class.rs
@@ -451,8 +451,12 @@ mod tests {
     fn macos_accepts_heap_addresses_below_two_tb() {
         // The Rust test harness has observed mimalloc allocations around
         // 45 GB. Classification is purely numeric and must not dereference
-        // this representative address.
-        assert!(is_valid_obj_ptr(0x0000_000a_0000_0000usize as *const u8));
+        // this representative address. In #8905 this gate was reached by the
+        // RegExp header-brand fallback across prebuilt-stdlib runtime copies;
+        // rejecting the address made dependency-side `.test()` dispatch miss.
+        let low_macos_heap_addr = 0x0000_000a_0000_0000usize;
+        assert!(is_valid_obj_ptr(low_macos_heap_addr as *const u8));
+        assert!(is_plausible_heap_addr(low_macos_heap_addr));
     }
 
     #[cfg(all(
diff --git a/crates/perry/tests/issue_8905_regexp_package_boundary.rs b/crates/perry/tests/issue_8905_regexp_package_boundary.rs
new file mode 100644
index 0000000000..8bb8c5ea25
--- /dev/null
+++ b/crates/perry/tests/issue_8905_regexp_package_boundary.rs
@@ -0,0 +1,153 @@
+//! Regression test for #8905: a RegExp passed into a `compilePackages`
+//! dependency must retain RegExp method behavior when the dependency reads it
+//! back through an object property.
+
+use std::path::PathBuf;
+use std::process::Command;
+use std::sync::Once;
+
+fn perry_bin() -> PathBuf {
+    PathBuf::from(env!("CARGO_BIN_EXE_perry"))
+}
+
+fn workspace_root() -> PathBuf {
+    PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../..")
+        .canonicalize()
+        .expect("canonicalize workspace root")
+}
+
+fn target_debug_dir() -> PathBuf {
+    let target = std::env::var_os("CARGO_TARGET_DIR")
+        .map(PathBuf::from)
+        .unwrap_or_else(|| workspace_root().join("target"));
+    if cfg!(windows) {
+        target.join("x86_64-pc-windows-msvc").join("debug")
+    } else {
+        target.join("debug")
+    }
+}
+
+fn ensure_runtime_archives() {
+    static BUILD_RUNTIME: Once = Once::new();
+    BUILD_RUNTIME.call_once(|| {
+        let cargo = std::env::var_os("CARGO").unwrap_or_else(|| "cargo".into());
+        let mut command = Command::new(cargo);
+        command
+            .current_dir(workspace_root())
+            .arg("build")
+            .arg("-p")
+            .arg("perry-runtime-static")
+            .arg("-p")
+            .arg("perry-stdlib-static");
+        if cfg!(windows) {
+            command.arg("--target").arg("x86_64-pc-windows-msvc");
+        }
+        let build = command.output().expect("build static runtime archives");
+        assert!(
+            build.status.success(),
+            "runtime archive build failed\nstdout:\n{}\nstderr:\n{}",
+            String::from_utf8_lossy(&build.stdout),
+            String::from_utf8_lossy(&build.stderr)
+        );
+    });
+}
+
+#[test]
+fn regexp_methods_survive_the_compiled_package_boundary() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let root = dir.path();
+
+    std::fs::write(
+        root.join("package.json"),
+        r#"{
+  "name": "regexp-package-boundary",
+  "private": true,
+  "type": "module",
+  "perry": {
+    "compilePackages": ["regex-consumer"],
+    "allow": { "compilePackages": ["regex-consumer"] }
+  }
+}"#,
+    )
+    .expect("write consumer package.json");
+
+    let package = root.join("node_modules/regex-consumer");
+    std::fs::create_dir_all(&package).expect("mkdir regex-consumer");
+    std::fs::write(
+        package.join("package.json"),
+        r#"{
+  "name": "regex-consumer",
+  "version": "1.0.0",
+  "type": "module",
+  "exports": "./index.js"
+}"#,
+    )
+    .expect("write dependency package.json");
+    std::fs::write(
+        package.join("index.js"),
+        r#"
+import { randomUUID } from "node:crypto";
+
+export function makeRegexCheck(def) {
+  return (value) => {
+    def.pattern.lastIndex = 0;
+    return def.pattern.test(value);
+  };
+}
+
+export function stdlibMarker() {
+  return typeof randomUUID;
+}
+"#,
+    )
+    .expect("write compiled dependency");
+
+    let entry = root.join("main.ts");
+    std::fs::write(
+        &entry,
+        r#"
+import { makeRegexCheck, stdlibMarker } from "regex-consumer";
+
+const check = makeRegexCheck({ pattern: /^a+$/ });
+console.log(stdlibMarker(), check("aaa"), check("bbb"));
+"#,
+    )
+    .expect("write entry");
+
+    // The node:crypto import forces the full-stdlib link used by the reporter.
+    // With PERRY_NO_AUTO_OPTIMIZE that can put a second statically linked
+    // runtime on the compiled-package side of this RegExp method call.
+    ensure_runtime_archives();
+    let output = root.join("main_bin");
+    let compile = Command::new(perry_bin())
+        .current_dir(root)
+        .arg("compile")
+        .arg(&entry)
+        .arg("-o")
+        .arg(&output)
+        .arg("--no-cache")
+        .env("PERRY_NO_AUTO_OPTIMIZE", "1")
+        .env("PERRY_RUNTIME_DIR", target_debug_dir())
+        .output()
+        .expect("run perry compile");
+    assert!(
+        compile.status.success(),
+        "perry compile failed\nstdout:\n{}\nstderr:\n{}",
+        String::from_utf8_lossy(&compile.stdout),
+        String::from_utf8_lossy(&compile.stderr)
+    );
+
+    let run = Command::new(&output).output().expect("run compiled binary");
+    assert!(
+        run.status.success(),
+        "compiled binary failed\nstatus: {:?}\nstdout:\n{}\nstderr:\n{}",
+        run.status,
+        String::from_utf8_lossy(&run.stdout),
+        String::from_utf8_lossy(&run.stderr)
+    );
+    assert_eq!(
+        String::from_utf8_lossy(&run.stdout),
+        "function true false\n"
+    );
+}