diff --git a/Cargo.lock b/Cargo.lock
index e41193896d3fd..20c2340aea9c4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -62,12 +62,6 @@ version = "0.7.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
 
-[[package]]
-name = "assert-unchecked"
-version = "0.1.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7330592adf847ee2e3513587b4db2db410a0d751378654e7e993d9adcbe5c795"
-
 [[package]]
 name = "async-trait"
 version = "0.1.88"
@@ -1548,9 +1542,9 @@ name = "oxc_allocator"
 version = "0.60.0"
 dependencies = [
  "allocator-api2",
- "assert-unchecked",
  "bumpalo",
  "hashbrown 0.15.2",
+ "oxc_data_structures",
  "oxc_estree",
  "rustc-hash",
  "serde",
@@ -1718,7 +1712,6 @@ dependencies = [
 name = "oxc_data_structures"
 version = "0.60.0"
 dependencies = [
- "assert-unchecked",
  "ropey",
 ]
 
@@ -1953,7 +1946,6 @@ dependencies = [
 name = "oxc_parser"
 version = "0.60.0"
 dependencies = [
- "assert-unchecked",
  "bitflags 2.9.0",
  "cow-utils",
  "memchr",
@@ -1962,6 +1954,7 @@ dependencies = [
  "oxc_allocator",
  "oxc_ast",
  "oxc_ast_visit",
+ "oxc_data_structures",
  "oxc_diagnostics",
  "oxc_ecmascript",
  "oxc_regular_expression",
@@ -2073,7 +2066,6 @@ dependencies = [
 name = "oxc_semantic"
 version = "0.60.0"
 dependencies = [
- "assert-unchecked",
  "insta",
  "itertools",
  "oxc_allocator",
@@ -2128,12 +2120,12 @@ dependencies = [
 name = "oxc_syntax"
 version = "0.60.0"
 dependencies = [
- "assert-unchecked",
  "bitflags 2.9.0",
  "cow-utils",
  "nonmax",
  "oxc_allocator",
  "oxc_ast_macros",
+ "oxc_data_structures",
  "oxc_estree",
  "oxc_index",
  "oxc_span",
diff --git a/Cargo.toml b/Cargo.toml
index 1f800673bb01a..f10b8a4359aeb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -158,7 +158,6 @@ oxc_sourcemap = "3"
 
 #
 allocator-api2 = "0.2.21"
-assert-unchecked = "0.1.2"
 base64 = "0.22.1"
 bitflags = "2.8.0"
 bpaf = "0.9.16"
diff --git a/crates/oxc_allocator/Cargo.toml b/crates/oxc_allocator/Cargo.toml
index 42f2e298957f3..c8315f8e5b299 100644
--- a/crates/oxc_allocator/Cargo.toml
+++ b/crates/oxc_allocator/Cargo.toml
@@ -19,10 +19,10 @@ workspace = true
 doctest = false
 
 [dependencies]
+oxc_data_structures = { workspace = true, features = ["assert_unchecked"] }
 oxc_estree = { workspace = true, optional = true }
 
 allocator-api2 = { workspace = true }
-assert-unchecked = { workspace = true }
 bumpalo = { workspace = true, features = ["allocator-api2", "collections"] }
 hashbrown = { workspace = true, default-features = false, features = ["inline-more", "allocator-api2"] }
 rustc-hash = { workspace = true }
diff --git a/crates/oxc_allocator/src/string.rs b/crates/oxc_allocator/src/string.rs
index be3506fa39b09..9d2abd13d4ebd 100644
--- a/crates/oxc_allocator/src/string.rs
+++ b/crates/oxc_allocator/src/string.rs
@@ -13,11 +13,12 @@ use std::{
     ptr,
 };
 
-use assert_unchecked::assert_unchecked;
 use bumpalo::collections::String as BumpaloString;
 pub use simdutf8::basic::Utf8Error;
 use simdutf8::basic::from_utf8;
 
+use oxc_data_structures::assert_unchecked;
+
 use crate::{Allocator, Vec};
 
 /// Arena String.
diff --git a/crates/oxc_data_structures/Cargo.toml b/crates/oxc_data_structures/Cargo.toml
index 7f240c2918aaa..a4b7d3fe128e7 100644
--- a/crates/oxc_data_structures/Cargo.toml
+++ b/crates/oxc_data_structures/Cargo.toml
@@ -18,16 +18,17 @@ workspace = true
 
 [lib]
 test = true
+# Doctests must be enabled for this crate as they are used to run compilation failure tests
 doctest = true
 
 [dependencies]
-assert-unchecked = { workspace = true, optional = true }
 ropey = { workspace = true, optional = true }
 
 [features]
 default = []
-all = ["code_buffer", "inline_string", "rope", "stack"]
-code_buffer = ["dep:assert-unchecked"]
+all = ["assert_unchecked", "code_buffer", "inline_string", "rope", "stack"]
+assert_unchecked = []
+code_buffer = ["assert_unchecked"]
 inline_string = []
 rope = ["dep:ropey"]
-stack = ["dep:assert-unchecked"]
+stack = ["assert_unchecked"]
diff --git a/crates/oxc_data_structures/src/assert_unchecked.rs b/crates/oxc_data_structures/src/assert_unchecked.rs
new file mode 100644
index 0000000000000..e9ddd75adbbb1
--- /dev/null
+++ b/crates/oxc_data_structures/src/assert_unchecked.rs
@@ -0,0 +1,102 @@
+//! `assert_unchecked!` macro.
+
+/// Macro that makes a soundness promise to the compiler that this condition always holds.
+///
+/// This is wrapper around [`std::hint::assert_unchecked`] which performs a standard safe `assert!`
+/// in debug builds, and accepts a format string for the error in that case.
+///
+/// See documentation for [`std::hint::assert_unchecked`] for further details.
+///
+/// This macro can be used in const context.
+///
+/// # SAFETY
+/// It is undefined behaviour if the condition evaluates to `false`.
+///
+/// # Examples
+/// ```
+/// // Requires `assert_unchecked` feature
+/// use oxc_data_structures::assert_unchecked;
+///
+/// /// Read first byte from a `&[u8]`, without bounds checks.
+/// ///
+/// /// # SAFETY
+/// /// Caller must ensure `slice` is not empty.
+/// unsafe fn first_unchecked(slice: &[u8]) -> u8 {
+///     // SAFETY: Caller guarantees `slice` is not empty
+///     unsafe {
+///         assert_unchecked!(!slice.is_empty(), "Oh no. Slice is empty.");
+///     }
+///     // Compiler elides the bounds check here. https://godbolt.org/z/xaGK8GzbG
+///     slice[0]
+/// }
+/// ```
+#[macro_export]
+macro_rules! assert_unchecked {
+    ($cond:expr) => (assert_unchecked!($cond,));
+    ($cond:expr, $($arg:tt)*) => ({
+        #[cfg(debug_assertions)]
+        {
+            const unsafe fn __needs_unsafe() {}
+            __needs_unsafe();
+            assert!($cond, $($arg)*);
+        }
+        #[cfg(not(debug_assertions))]
+        {
+            std::hint::assert_unchecked($cond);
+        }
+    })
+}
+
+/**
+Doctest to ensure macro cannot be used without `unsafe {}`.
+```compile_fail
+use oxc_data_structures::assert_unchecked;
+assert_unchecked!(true);
+```
+*/
+const _MACRO_CANNOT_BE_USED_WITHOUT_UNSAFE: () = ();
+
+#[cfg(test)]
+#[expect(clippy::undocumented_unsafe_blocks)]
+mod test {
+    mod pass {
+        use crate::assert_unchecked;
+
+        #[test]
+        fn plain() {
+            unsafe { assert_unchecked!(0 == 0) };
+        }
+
+        #[test]
+        fn string_literal() {
+            unsafe { assert_unchecked!(0 == 0, "String literal") };
+        }
+
+        #[test]
+        fn fmt_string() {
+            unsafe { assert_unchecked!(0 == 0, "Format str {} {:?}", 123, 456) };
+        }
+    }
+
+    // Cannot test failing assertions in release mode as it'd be undefined behavior!
+    #[cfg(debug_assertions)]
+    mod fail {
+        #[test]
+        #[should_panic(expected = "assertion failed: 0 == 1")]
+        fn plain() {
+            unsafe { assert_unchecked!(0 == 1) };
+        }
+
+        #[test]
+        #[should_panic(expected = "String literal")]
+        fn string_literal() {
+            unsafe { assert_unchecked!(0 == 1, "String literal") };
+        }
+
+        #[test]
+        #[should_panic(expected = "Format str: 123 456")]
+        fn fmt_string() {
+            unsafe { assert_unchecked!(0 == 1, "Format str: {} {:?}", 123, 456) };
+        }
+    }
+}
diff --git a/crates/oxc_data_structures/src/code_buffer.rs b/crates/oxc_data_structures/src/code_buffer.rs
index ab6f2d06d4270..b46c789cebb48 100644
--- a/crates/oxc_data_structures/src/code_buffer.rs
+++ b/crates/oxc_data_structures/src/code_buffer.rs
@@ -2,7 +2,7 @@
 
 use std::iter;
 
-use assert_unchecked::assert_unchecked;
+use crate::assert_unchecked;
 
 /// A string builder for constructing source code.
 ///
diff --git a/crates/oxc_data_structures/src/lib.rs b/crates/oxc_data_structures/src/lib.rs
index f4e47146dd173..76309e61864db 100644
--- a/crates/oxc_data_structures/src/lib.rs
+++ b/crates/oxc_data_structures/src/lib.rs
@@ -2,11 +2,17 @@
 
 #![warn(missing_docs)]
 
+#[cfg(feature = "assert_unchecked")]
+mod assert_unchecked;
+
 #[cfg(feature = "code_buffer")]
 pub mod code_buffer;
+
 #[cfg(feature = "inline_string")]
 pub mod inline_string;
+
 #[cfg(feature = "rope")]
 pub mod rope;
+
 #[cfg(feature = "stack")]
 pub mod stack;
diff --git a/crates/oxc_data_structures/src/stack/common.rs b/crates/oxc_data_structures/src/stack/common.rs
index ba3286362d269..005403a6f42eb 100644
--- a/crates/oxc_data_structures/src/stack/common.rs
+++ b/crates/oxc_data_structures/src/stack/common.rs
@@ -5,7 +5,7 @@ use std::{
     slice,
 };
 
-use assert_unchecked::assert_unchecked;
+use crate::assert_unchecked;
 
 use super::StackCapacity;
 
diff --git a/crates/oxc_parser/Cargo.toml b/crates/oxc_parser/Cargo.toml
index bb37450cd9844..475dfeeeab0b6 100644
--- a/crates/oxc_parser/Cargo.toml
+++ b/crates/oxc_parser/Cargo.toml
@@ -21,13 +21,13 @@ doctest = false
 [dependencies]
 oxc_allocator = { workspace = true }
 oxc_ast = { workspace = true }
+oxc_data_structures = { workspace = true, features = ["assert_unchecked"] }
 oxc_diagnostics = { workspace = true }
 oxc_ecmascript = { workspace = true }
 oxc_regular_expression = { workspace = true }
 oxc_span = { workspace = true }
 oxc_syntax = { workspace = true }
 
-assert-unchecked = { workspace = true }
 bitflags = { workspace = true }
 cow-utils = { workspace = true }
 num-bigint = { workspace = true }
diff --git a/crates/oxc_parser/src/lexer/byte_handlers.rs b/crates/oxc_parser/src/lexer/byte_handlers.rs
index 3057e3b7339ac..f87a9062c08f3 100644
--- a/crates/oxc_parser/src/lexer/byte_handlers.rs
+++ b/crates/oxc_parser/src/lexer/byte_handlers.rs
@@ -108,7 +108,7 @@ macro_rules! byte_handler {
 ///   fn SPS(lexer: &mut Lexer) {
 ///     // SAFETY: This macro is only used for ASCII characters
 ///     unsafe {
-///       use assert_unchecked::assert_unchecked;
+///       use oxc_data_structures::assert_unchecked;
 ///       assert_unchecked!(!lexer.source.is_eof());
 ///       assert_unchecked!(lexer.source.peek_byte_unchecked() < 128);
 ///     }
@@ -125,7 +125,7 @@ macro_rules! ascii_byte_handler {
         byte_handler!($id($lex) {
             // SAFETY: This macro is only used for ASCII characters
             unsafe {
-                use assert_unchecked::assert_unchecked;
+                use oxc_data_structures::assert_unchecked;
                 assert_unchecked!(!$lex.source.is_eof());
                 assert_unchecked!($lex.source.peek_byte_unchecked() < 128);
             }
diff --git a/crates/oxc_semantic/Cargo.toml b/crates/oxc_semantic/Cargo.toml
index f5ca7c83da87e..587d19e2ae003 100644
--- a/crates/oxc_semantic/Cargo.toml
+++ b/crates/oxc_semantic/Cargo.toml
@@ -23,14 +23,13 @@ oxc_allocator = { workspace = true }
 oxc_ast = { workspace = true }
 oxc_ast_visit = { workspace = true }
 oxc_cfg = { workspace = true }
-oxc_data_structures = { workspace = true, features = ["stack"] }
+oxc_data_structures = { workspace = true, features = ["assert_unchecked", "stack"] }
 oxc_diagnostics = { workspace = true }
 oxc_ecmascript = { workspace = true }
 oxc_index = { workspace = true }
 oxc_span = { workspace = true }
 oxc_syntax = { workspace = true }
 
-assert-unchecked = { workspace = true }
 itertools = { workspace = true }
 phf = { workspace = true, features = ["macros"] }
 rustc-hash = { workspace = true }
diff --git a/crates/oxc_semantic/src/unresolved_stack.rs b/crates/oxc_semantic/src/unresolved_stack.rs
index 344802c8ac223..934cba4530058 100644
--- a/crates/oxc_semantic/src/unresolved_stack.rs
+++ b/crates/oxc_semantic/src/unresolved_stack.rs
@@ -1,6 +1,6 @@
-use assert_unchecked::assert_unchecked;
 use rustc_hash::FxHashMap;
 
+use oxc_data_structures::assert_unchecked;
 use oxc_span::Atom;
 use oxc_syntax::reference::ReferenceId;
 
diff --git a/crates/oxc_syntax/Cargo.toml b/crates/oxc_syntax/Cargo.toml
index 03851b1ac5d9b..68b4bcdcd43b2 100644
--- a/crates/oxc_syntax/Cargo.toml
+++ b/crates/oxc_syntax/Cargo.toml
@@ -22,11 +22,11 @@ doctest = false
 [dependencies]
 oxc_allocator = { workspace = true }
 oxc_ast_macros = { workspace = true }
+oxc_data_structures = { workspace = true, features = ["assert_unchecked"] }
 oxc_estree = { workspace = true }
 oxc_index = { workspace = true }
 oxc_span = { workspace = true }
 
-assert-unchecked = { workspace = true }
 bitflags = { workspace = true }
 cow-utils = { workspace = true }
 nonmax = { workspace = true }
diff --git a/crates/oxc_syntax/src/identifier.rs b/crates/oxc_syntax/src/identifier.rs
index 1685dd9c0984e..983a1c4eca300 100644
--- a/crates/oxc_syntax/src/identifier.rs
+++ b/crates/oxc_syntax/src/identifier.rs
@@ -1,7 +1,9 @@
 #![expect(missing_docs)] // fixme
-use assert_unchecked::assert_unchecked;
+
 use unicode_id_start::{is_id_continue_unicode, is_id_start_unicode};
 
+use oxc_data_structures::assert_unchecked;
+
 pub const EOF: char = '\0';
 
 // 11.1 Unicode Format-Control Characters