diff --git a/src/bun_core/string/immutable.rs b/src/bun_core/string/immutable.rs
index fc8727ea789a..cdf59aeb9e30 100644
--- a/src/bun_core/string/immutable.rs
+++ b/src/bun_core/string/immutable.rs
@@ -377,31 +377,10 @@ pub use crate::strings_impl::{
     to_utf8_from_latin1_z, u16_lead, u16_trail,
 };
 
-/// memmem — libc on posix, scalar fallback on windows.
-#[cfg(not(windows))]
-pub fn memmem(haystack: &[u8], needle: &[u8]) -> Option<usize> {
-    if needle.is_empty() {
-        return Some(0);
-    }
-    // SAFETY: `&[u8]` guarantees both (ptr,len) pairs are valid for reads;
-    // libc memmem only reads within those bounds.
-    let p = unsafe {
-        libc::memmem(
-            haystack.as_ptr().cast(),
-            haystack.len(),
-            needle.as_ptr().cast(),
-            needle.len(),
-        )
-    };
-    if p.is_null() {
-        None
-    } else {
-        Some(p as usize - haystack.as_ptr() as usize)
-    }
-}
-#[cfg(windows)]
+/// memmem — `highway_memmem` (HWY_DYNAMIC_DISPATCH MemMemImpl), same on all platforms.
+#[inline]
 pub fn memmem(haystack: &[u8], needle: &[u8]) -> Option<usize> {
-    bstr::ByteSlice::find(haystack, needle)
+    highway::memmem(haystack, needle)
 }
 
 /// `bun.reinterpretSlice` — `&[T]` → `&[u8]` view (T must be u8/u16 in practice).
diff --git a/src/highway/lib.rs b/src/highway/lib.rs
index 68f9875cb464..32ddd18bed0e 100644
--- a/src/highway/lib.rs
+++ b/src/highway/lib.rs
@@ -6,6 +6,13 @@ unsafe extern "C" {
 
     fn highway_index_of_char(haystack: *const u8, haystack_len: usize, needle: u8) -> usize;
 
+    fn highway_memmem(
+        haystack: *const u8,
+        haystack_len: usize,
+        needle: *const u8,
+        needle_len: usize,
+    ) -> *const u8;
+
     fn highway_index_of_interesting_character_in_string_literal(
         text: *const u8,
         text_len: usize,
@@ -140,6 +147,31 @@ pub fn index_of_char(haystack: &[u8], needle: u8) -> Option<usize> {
     Some(result)
 }
 
+#[inline(always)]
+pub fn memmem(haystack: &[u8], needle: &[u8]) -> Option<usize> {
+    if needle.is_empty() {
+        return Some(0);
+    }
+    if haystack.len() < needle.len() {
+        return None;
+    }
+    // SAFETY: both (ptr,len) pairs are valid readable ranges.
+    let p = unsafe {
+        highway_memmem(
+            haystack.as_ptr(),
+            haystack.len(),
+            needle.as_ptr(),
+            needle.len(),
+        )
+    };
+    if p.is_null() {
+        None
+    } else {
+        // SAFETY: highway_memmem returns a pointer within `haystack` on success.
+        Some(unsafe { p.offset_from(haystack.as_ptr()) } as usize)
+    }
+}
+
 #[inline(always)]
 pub fn index_of_interesting_character_in_string_literal(
     slice: &[u8],