diff --git a/src/native/corehost/browserhost/loader/index.ts b/src/native/corehost/browserhost/loader/index.ts
index db7a8fb61f787c..c1988d51328b87 100644
--- a/src/native/corehost/browserhost/loader/index.ts
+++ b/src/native/corehost/browserhost/loader/index.ts
@@ -16,7 +16,7 @@ import GitHash from "consts:gitHash";
 import { loaderConfig, getLoaderConfig } from "./config";
 import { exit, isExited, isRuntimeRunning, addOnExitListener, registerExit, quitNow } from "./exit";
 import { invokeLibraryInitializers } from "./lib-initializers";
-import { check, error, info, warn, debug } from "./logging";
+import { check, error, info, warn, debug, fastCheck } from "./logging";
 
 import { dotnetAssert, dotnetLoaderExports, dotnetLogger, dotnetUpdateInternals, dotnetUpdateInternalsSubscriber } from "./cross-module";
 import { rejectRunMainPromise, resolveRunMainPromise, getRunMainPromise, abortStartup } from "./run";
@@ -77,6 +77,7 @@ export function dotnetInitializeModule(): RuntimeAPI {
     Object.assign(dotnetLogger, logger);
     const assert: AssertType = {
         check,
+        fastCheck,
     };
     Object.assign(dotnetAssert, assert);
 
@@ -99,6 +100,7 @@ export function dotnetInitializeModule(): RuntimeAPI {
             logger.warn,
             logger.error,
             assert.check,
+            assert.fastCheck,
             dotnetLoaderExports.resolveRunMainPromise,
             dotnetLoaderExports.rejectRunMainPromise,
             dotnetLoaderExports.getRunMainPromise,
diff --git a/src/native/corehost/browserhost/loader/logging.ts b/src/native/corehost/browserhost/loader/logging.ts
index ce6ab84cf94f6e..ee20d8e6008f06 100644
--- a/src/native/corehost/browserhost/loader/logging.ts
+++ b/src/native/corehost/browserhost/loader/logging.ts
@@ -1,11 +1,18 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-// WASM-TODO: inline the code
+export function check(condition: unknown, message: string): asserts condition {
+    if (!condition) {
+        throw new Error(`dotnetAssert failed: ${message}`);
+    }
+}
 
-export function check(condition: unknown, messageFactory: string | (() => string)): asserts condition {
+// calls to fastCheck will be inlined by rollup
+// so that the string formatting or allocation of a closure would only happen in failure cases
+// this is important for performance sensitive code paths
+export function fastCheck(condition: unknown, messageFactory: (() => string)): asserts condition {
     if (!condition) {
-        const message = typeof messageFactory === "string" ? messageFactory : messageFactory();
+        const message = messageFactory();
         throw new Error(`dotnetAssert failed: ${message}`);
     }
 }
diff --git a/src/native/libs/Common/JavaScript/cross-module/index.ts b/src/native/libs/Common/JavaScript/cross-module/index.ts
index f89b3a73f12793..1118680637d06e 100644
--- a/src/native/libs/Common/JavaScript/cross-module/index.ts
+++ b/src/native/libs/Common/JavaScript/cross-module/index.ts
@@ -110,19 +110,20 @@ export function dotnetUpdateInternalsSubscriber() {
         };
         const assertLocal: AssertType = {
             check: table[4],
+            fastCheck: table[5],
         };
         const loaderExportsLocal: LoaderExports = {
-            resolveRunMainPromise: table[5],
-            rejectRunMainPromise: table[6],
-            getRunMainPromise: table[7],
-            createPromiseCompletionSource: table[8],
-            isControllablePromise: table[9],
-            getPromiseCompletionSource: table[10],
-            isExited: table[11],
-            isRuntimeRunning: table[12],
-            addOnExitListener: table[13],
-            abortStartup: table[14],
-            quitNow: table[15],
+            resolveRunMainPromise: table[6],
+            rejectRunMainPromise: table[7],
+            getRunMainPromise: table[8],
+            createPromiseCompletionSource: table[9],
+            isControllablePromise: table[10],
+            getPromiseCompletionSource: table[11],
+            isExited: table[12],
+            isRuntimeRunning: table[13],
+            addOnExitListener: table[14],
+            abortStartup: table[15],
+            quitNow: table[16],
         };
         Object.assign(dotnetLoaderExports, loaderExportsLocal);
         Object.assign(logger, loggerLocal);
diff --git a/src/native/libs/Common/JavaScript/types/exchange.ts b/src/native/libs/Common/JavaScript/types/exchange.ts
index b65e8264a94c72..f1043e438d7e15 100644
--- a/src/native/libs/Common/JavaScript/types/exchange.ts
+++ b/src/native/libs/Common/JavaScript/types/exchange.ts
@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-import type { check, error, info, warn, debug } from "../../../../corehost/browserhost/loader/logging";
+import type { check, error, info, warn, debug, fastCheck } from "../../../../corehost/browserhost/loader/logging";
 import type { resolveRunMainPromise, rejectRunMainPromise, getRunMainPromise, abortStartup } from "../../../../corehost/browserhost/loader/run";
 import type { addOnExitListener, isExited, isRuntimeRunning, quitNow } from "../../../../corehost/browserhost/loader/exit";
 
@@ -29,6 +29,7 @@ export type LoggerType = {
 
 export type AssertType = {
     check: typeof check,
+    fastCheck: typeof fastCheck,
 }
 
 export type LoaderExports = {
@@ -51,6 +52,7 @@ export type LoaderExportsTable = [
     typeof warn,
     typeof error,
     typeof check,
+    typeof fastCheck,
     typeof resolveRunMainPromise,
     typeof rejectRunMainPromise,
     typeof getRunMainPromise,
diff --git a/src/native/libs/System.Native.Browser/utils/memory.ts b/src/native/libs/System.Native.Browser/utils/memory.ts
index 9b9fb60dd0c617..550801544ec23e 100644
--- a/src/native/libs/System.Native.Browser/utils/memory.ts
+++ b/src/native/libs/System.Native.Browser/utils/memory.ts
@@ -9,8 +9,8 @@ const min_int64_big = BigInt("-9223372036854775808");
 const sharedArrayBufferDefined = typeof SharedArrayBuffer !== "undefined";
 
 export function assertIntInRange(value: Number, min: Number, max: Number) {
-    dotnetAssert.check(Number.isSafeInteger(value), () => `Value is not an integer: ${value} (${typeof (value)})`);
-    dotnetAssert.check(value >= min && value <= max, () => `Overflow: value ${value} is out of ${min} ${max} range`);
+    dotnetAssert.fastCheck(Number.isSafeInteger(value), () => `Value is not an integer: ${value} (${typeof (value)})`);
+    dotnetAssert.fastCheck(value >= min && value <= max, () => `Overflow: value ${value} is out of ${min} ${max} range`);
 }
 
 /** note: boolean is 8 bits not 32 bits when inside a structure or array */
@@ -82,7 +82,7 @@ export function setHeapI32(offset: MemOffset, value: number): void {
  * Throws for values which are not 52 bit integer. See Number.isSafeInteger()
  */
 export function setHeapI52(offset: MemOffset, value: number): void {
-    dotnetAssert.check(Number.isSafeInteger(value), () => `Value is not a safe integer: ${value} (${typeof (value)})`);
+    dotnetAssert.fastCheck(Number.isSafeInteger(value), () => `Value is not a safe integer: ${value} (${typeof (value)})`);
     throw new Error("WASM-TODO");
 }
 
@@ -90,25 +90,25 @@ export function setHeapI52(offset: MemOffset, value: number): void {
  * Throws for values which are not 52 bit integer or are negative. See Number.isSafeInteger().
  */
 export function setHeapU52(offset: MemOffset, value: number): void {
-    dotnetAssert.check(Number.isSafeInteger(value), () => `Value is not a safe integer: ${value} (${typeof (value)})`);
-    dotnetAssert.check(value >= 0, "Can't convert negative Number into UInt64");
+    dotnetAssert.fastCheck(Number.isSafeInteger(value), () => `Value is not a safe integer: ${value} (${typeof (value)})`);
+    dotnetAssert.fastCheck(value >= 0, () => "Can't convert negative Number into UInt64");
     throw new Error("WASM-TODO");
 }
 
 export function setHeapI64Big(offset: MemOffset, value: bigint): void {
-    dotnetAssert.check(typeof value === "bigint", () => `Value is not an bigint: ${value} (${typeof (value)})`);
-    dotnetAssert.check(value >= min_int64_big && value <= max_int64_big, () => `Overflow: value ${value} is out of ${min_int64_big} ${max_int64_big} range`);
+    dotnetAssert.fastCheck(typeof value === "bigint", () => `Value is not an bigint: ${value} (${typeof (value)})`);
+    dotnetAssert.fastCheck(value >= min_int64_big && value <= max_int64_big, () => `Overflow: value ${value} is out of ${min_int64_big} ${max_int64_big} range`);
 
     Module.HEAP64[<any>offset >>> 3] = value;
 }
 
 export function setHeapF32(offset: MemOffset, value: number): void {
-    dotnetAssert.check(typeof value === "number", () => `Value is not a Number: ${value} (${typeof (value)})`);
+    dotnetAssert.fastCheck(typeof value === "number", () => `Value is not a Number: ${value} (${typeof (value)})`);
     Module.HEAPF32[<any>offset >>> 2] = value;
 }
 
 export function setHeapF64(offset: MemOffset, value: number): void {
-    dotnetAssert.check(typeof value === "number", () => `Value is not a Number: ${value} (${typeof (value)})`);
+    dotnetAssert.fastCheck(typeof value === "number", () => `Value is not a Number: ${value} (${typeof (value)})`);
     Module.HEAPF64[<any>offset >>> 3] = value;
 }
 
diff --git a/src/native/rollup.config.defines.js b/src/native/rollup.config.defines.js
index aa0d31c92e4892..b4bc4f859b4348 100644
--- a/src/native/rollup.config.defines.js
+++ b/src/native/rollup.config.defines.js
@@ -52,3 +52,15 @@ export const envConstants = {
     gitHash,
     isContinuousIntegrationBuild,
 };
+
+/* eslint-disable quotes */
+export const inlinefastCheck = [
+    {
+        pattern: 'dotnetAssert\\.fastCheck\\(([^,]*), \\(\\) => *`([^`]*)`\\);',
+        replacement: (match) => `if (!(${match[1]})) throw new Error(\`Assert failed: ${match[2]}\`); // inlined fastCheck`
+    },
+    {
+        pattern: 'dotnetAssert\\.fastCheck\\(([^,]*), \\(\\) => *"([^"]*)"\\);',
+        replacement: (match) => `if (!(${match[1]})) throw new Error(\`Assert failed: ${match[2]}\`); // inlined fastCheck`
+    },
+];
diff --git a/src/native/rollup.config.js b/src/native/rollup.config.js
index 24ec8ce9f30414..241403ff6546bd 100644
--- a/src/native/rollup.config.js
+++ b/src/native/rollup.config.js
@@ -8,9 +8,10 @@ import dts from "rollup-plugin-dts";
 import {
     externalDependencies, envConstants, banner, banner_dts,
     isDebug, staticLibDestination,
-    keep_classnames, keep_fnames, reserved
+    keep_classnames, keep_fnames, reserved,
+    inlinefastCheck,
 } from "./rollup.config.defines.js";
-import { terserPlugin, writeOnChangePlugin, consts, onwarn, alwaysLF, iife2fe, emsAmbient, sourcemapPathTransform } from "./rollup.config.plugins.js";
+import { terserPlugin, writeOnChangePlugin, consts, onwarn, alwaysLF, iife2fe, emsAmbient, regexReplace, sourcemapPathTransform } from "./rollup.config.plugins.js";
 import { promises as fs } from "fs";
 
 const dotnetDTS = {
@@ -189,6 +190,7 @@ function configure({ input, output, terser, external }) {
         external: external ? [...external, ...externalDependencies] : externalDependencies,
         plugins: [
             nodeResolve(),
+            regexReplace([...inlinefastCheck]),
             consts(envConstants),
             typescript({
                 tsconfig: "./tsconfig.json",
diff --git a/src/native/rollup.config.plugins.js b/src/native/rollup.config.plugins.js
index 7eac65e1df23a8..faeabfe01ed734 100644
--- a/src/native/rollup.config.plugins.js
+++ b/src/native/rollup.config.plugins.js
@@ -7,6 +7,7 @@ import virtual from "@rollup/plugin-virtual";
 import * as fs from "fs";
 import * as path from "path";
 import terser from "@rollup/plugin-terser";
+import MagicString from "magic-string";
 
 import { isContinuousIntegrationBuild, gitHash } from "./rollup.config.defines.js";
 
@@ -36,6 +37,50 @@ export const writeOnChangePlugin = () => ({
     generateBundle: writeWhenChanged
 });
 
+export function regexReplace(replacements = []) {
+    return {
+        name: "regexReplace",
+
+        renderChunk(code, chunk) {
+            const id = chunk.fileName;
+            return executeReplacement(this, code, id);
+        },
+
+        transform(code, id) {
+            return executeReplacement(this, code, id);
+        }
+    };
+
+    function executeReplacement(_, code, id) {
+        const magicString = new MagicString(code);
+        if (!codeHasReplacements(code, id, magicString)) {
+            return null;
+        }
+
+        const result = { code: magicString.toString() };
+        result.map = magicString.generateMap({ hires: true });
+        return result;
+    }
+
+    function codeHasReplacements(code, id, magicString) {
+        let result = false;
+        let match;
+        for (const rep of replacements) {
+            const { pattern, replacement } = rep;
+            const rx = new RegExp(pattern, "gm");
+            while ((match = rx.exec(code))) {
+                result = true;
+                const updated = replacement(match);
+                const start = match.index;
+                const end = start + match[0].length;
+                magicString.overwrite(start, end, updated);
+            }
+        }
+
+        return result;
+    }
+}
+
 // Drop invocation from IIFE
 export function iife2fe() {
     return {
@@ -45,10 +90,10 @@ export function iife2fe() {
             if (name.endsWith(".map")) return;
             const asset = bundle[name];
             const code = asset.code;
-            //throw new Error("iife2fe " + code);
             asset.code = code
-                .replace(/}\({}\);/, "};") // }({}); ->};
-                .replace(/}\)\({}\);/, "});"); // })({}); ->});
+                // spaces are there to preserve source mappings
+                .replace(/}\({}\);/, "}    ;") // }({}); -> }    ;
+                .replace(/}\)\({}\);/, "})     ;"); // })({}); -> })     ;
         }
     };
 }