diff --git a/cli/tests/unit/webstorage_test.ts b/cli/tests/unit/webstorage_test.ts
index 25813ac037..e6ca5bb880 100644
--- a/cli/tests/unit/webstorage_test.ts
+++ b/cli/tests/unit/webstorage_test.ts
@@ -1,7 +1,7 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 // deno-lint-ignore-file no-explicit-any
 
-import { assert } from "./test_util.ts";
+import { assert, assertThrows } from "./test_util.ts";
 
 Deno.test({ permissions: "none" }, function webStoragesReassignable() {
   // Can reassign to web storages
@@ -11,3 +11,32 @@ Deno.test({ permissions: "none" }, function webStoragesReassignable() {
   assert(globalThis.localStorage instanceof globalThis.Storage);
   assert(globalThis.sessionStorage instanceof globalThis.Storage);
 });
+
+Deno.test(function webstorageSizeLimit() {
+  localStorage.clear();
+  assertThrows(
+    () => {
+      localStorage.setItem("k", "v".repeat(15 * 1024 * 1024));
+    },
+    Error,
+    "Exceeded maximum storage size",
+  );
+  assert(localStorage.getItem("k") === null);
+  assertThrows(
+    () => {
+      localStorage.setItem("k".repeat(15 * 1024 * 1024), "v");
+    },
+    Error,
+    "Exceeded maximum storage size",
+  );
+  assertThrows(
+    () => {
+      localStorage.setItem(
+        "k".repeat(5 * 1024 * 1024),
+        "v".repeat(5 * 1024 * 1024),
+      );
+    },
+    Error,
+    "Exceeded maximum storage size",
+  );
+});
diff --git a/ext/webstorage/lib.rs b/ext/webstorage/lib.rs
index e98b5da411..ca96b01bc1 100644
--- a/ext/webstorage/lib.rs
+++ b/ext/webstorage/lib.rs
@@ -19,7 +19,7 @@ pub use rusqlite;
 #[derive(Clone)]
 struct OriginStorageDir(PathBuf);
 
-const MAX_STORAGE_BYTES: u32 = 10 * 1024 * 1024;
+const MAX_STORAGE_BYTES: usize = 10 * 1024 * 1024;
 
 pub fn init(origin_storage_dir: Option<PathBuf>) -> Extension {
   Extension::builder_with_deps(env!("CARGO_PKG_NAME"), &["deno_webidl"])
@@ -133,6 +133,20 @@ pub fn op_webstorage_key(
   Ok(key)
 }
 
+#[inline]
+fn size_check(input: usize) -> Result<(), AnyError> {
+  if input >= MAX_STORAGE_BYTES {
+    return Err(
+      deno_web::DomExceptionQuotaExceededError::new(
+        "Exceeded maximum storage size",
+      )
+      .into(),
+    );
+  }
+
+  Ok(())
+}
+
 #[op]
 pub fn op_webstorage_set(
   state: &mut OpState,
@@ -142,18 +156,13 @@ pub fn op_webstorage_set(
 ) -> Result<(), AnyError> {
   let conn = get_webstorage(state, persistent)?;
 
+  size_check(key.len() + value.len())?;
+
   let mut stmt = conn
     .prepare_cached("SELECT SUM(pgsize) FROM dbstat WHERE name = 'data'")?;
   let size: u32 = stmt.query_row(params![], |row| row.get(0))?;
 
-  if size >= MAX_STORAGE_BYTES {
-    return Err(
-      deno_web::DomExceptionQuotaExceededError::new(
-        "Exceeded maximum storage size",
-      )
-      .into(),
-    );
-  }
+  size_check(size as usize)?;
 
   let mut stmt = conn
     .prepare_cached("INSERT OR REPLACE INTO data (key, value) VALUES (?, ?)")?;