diff --git a/Cargo.lock b/Cargo.lock
index d91d84fa0a8..c5f93c9eb70 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -372,6 +372,7 @@ dependencies = [
  "boa_string",
  "bytemuck",
  "cfg-if",
+ "cow-utils",
  "criterion",
  "dashmap",
  "either",
@@ -921,6 +922,12 @@ dependencies = [
  "libm",
 ]
 
+[[package]]
+name = "cow-utils"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "417bef24afe1460300965a25ff4a24b8b45ad011948302ec221e8a0a81eb2c79"
+
 [[package]]
 name = "crc32fast"
 version = "1.4.2"
diff --git a/Cargo.toml b/Cargo.toml
index b411f795297..4622de3ae10 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -50,6 +50,7 @@ arbitrary = "1"
 bitflags = "2.5.0"
 clap = "4.5.23"
 colored = "2.2.0"
+cow-utils = "0.1.3"
 fast-float2 = "0.2.3"
 hashbrown = "0.15.2"
 indexmap = { version = "2.7.0", default-features = false }
diff --git a/clippy.toml b/clippy.toml
index 272425dad89..59ef99e1fe1 100644
--- a/clippy.toml
+++ b/clippy.toml
@@ -1,2 +1,5 @@
 doc-valid-idents = ['ECMAScript', 'JavaScript', 'SpiderMonkey', 'GitHub']
 allow-print-in-tests = true
+disallowed-methods = [
+  { path = "str::to_ascii_uppercase", reason = "To avoid memory allocation, use `cow_utils::CowUtils::cow_to_ascii_uppercase` instead." },
+]
diff --git a/core/engine/Cargo.toml b/core/engine/Cargo.toml
index 9a0d603e427..e6b225ebadf 100644
--- a/core/engine/Cargo.toml
+++ b/core/engine/Cargo.toml
@@ -75,6 +75,7 @@ boa_macros.workspace = true
 boa_ast.workspace = true
 boa_parser.workspace = true
 boa_string.workspace = true
+cow-utils.workspace = true
 serde = { workspace = true, features = ["derive", "rc"] }
 serde_json.workspace = true
 rand.workspace = true
diff --git a/core/engine/src/builtins/temporal/time_zone/mod.rs b/core/engine/src/builtins/temporal/time_zone/mod.rs
index a1d499e5829..2e73f0a2e0c 100644
--- a/core/engine/src/builtins/temporal/time_zone/mod.rs
+++ b/core/engine/src/builtins/temporal/time_zone/mod.rs
@@ -2,7 +2,7 @@
 #![allow(dead_code)]
 
 use crate::{builtins::temporal::to_zero_padded_decimal_string, Context};
-
+use cow_utils::CowUtils;
 // -- TimeZone Abstract Operations --
 
 /// Abstract operation `DefaultTimeZone ( )`
@@ -96,7 +96,7 @@ fn canonicalize_time_zone_name(time_zone: &str) -> String {
     // do not include local political rules for any time zones performs the following steps when
     // called:
     // 1. Assert: timeZone is an ASCII-case-insensitive match for "UTC".
-    assert_eq!(time_zone.to_ascii_uppercase(), "UTC");
+    assert_eq!(time_zone.cow_to_ascii_uppercase(), "UTC");
     // 2. Return "UTC".
     "UTC".to_owned()
 }