diff --git a/src/bindings/js.ts b/src/bindings/js.ts
index 52f0e6d08d..a38d90c4ec 100644
--- a/src/bindings/js.ts
+++ b/src/bindings/js.ts
@@ -949,6 +949,7 @@ export class JSBuilder extends ExportsWalker {
   /** Lifts a WebAssembly value to a JavaScript value. */
   makeLiftFromValue(name: string, type: Type, sb: string[] = this.sb): void {
     if (type.isInternalReference) {
+      // Lift reference types
       const clazz = assert(type.getClassOrWrapper(this.program));
       if (clazz.extends(this.program.arrayBufferInstance.prototype)) {
         sb.push("__liftBuffer(");
@@ -1005,11 +1006,13 @@ export class JSBuilder extends ExportsWalker {
       }
       sb.push(")");
     } else {
-      sb.push(name);
-      if (type.isUnsignedIntegerValue && type.size == 32) {
-        sb.push(" >>> 0");
-      } else if (type == Type.bool) {
-        sb.push(" != 0");
+      // Lift basic plain types
+      if (type == Type.bool) {
+        sb.push(`${name} != 0`);
+      } else if (type.isUnsignedIntegerValue && type.size >= 32) {
+        sb.push(type.size == 64 ? `BigInt.asUintN(64, ${name})` : `${name} >>> 0`);
+      } else {
+        sb.push(name);
       }
     }
   }
@@ -1017,6 +1020,7 @@ export class JSBuilder extends ExportsWalker {
   /** Lowers a JavaScript value to a WebAssembly value. */
   makeLowerToValue(name: string, type: Type, sb: string[] = this.sb): void {
     if (type.isInternalReference) {
+      // Lower reference types
       const clazz = assert(type.getClass());
       if (clazz.extends(this.program.arrayBufferInstance.prototype)) {
         sb.push("__lowerBuffer(");
@@ -1082,6 +1086,7 @@ export class JSBuilder extends ExportsWalker {
         sb.push(" || __notnull()");
       }
     } else {
+      // Lower basic types
       sb.push(name); // basic value
       if (type.isIntegerValue && type.size == 64) {
         sb.push(" || 0n");
@@ -1278,15 +1283,16 @@ enum Mode {
 
 function isPlainValue(type: Type, kind: Mode): bool {
   if (kind == Mode.IMPORT) {
-    // requires coercion of undefined to 0n
-    if (type.isIntegerValue && type.size == 64) return false;
     // may be stored to an Uint8Array, make sure to store 1/0
     if (type == Type.bool) return false;
+    // requires coercion of undefined to 0n
+    if (type.isIntegerValue && type.size == 64) return false;
   } else {
-    // requires coercion from signed to unsigned
-    if (type.isUnsignedIntegerValue && type.size == 32) return false;
     // requires coercion from 1/0 to true/false
     if (type == Type.bool) return false;
+    // requires coercion from signed to unsigned for u32 and u64.
+    // Note, u8 and u16 doesn't overflow in native type so mark as plain
+    if (type.isUnsignedIntegerValue && type.size >= 32) return false;
   }
   return !type.isInternalReference;
 }
@@ -1294,10 +1300,10 @@ function isPlainValue(type: Type, kind: Mode): bool {
 function isPlainFunction(signature: Signature, mode: Mode): bool {
   var parameterTypes = signature.parameterTypes;
   var inverseMode = mode == Mode.IMPORT ? Mode.EXPORT : Mode.IMPORT;
+  if (!isPlainValue(signature.returnType, mode)) return false;
   for (let i = 0, k = parameterTypes.length; i < k; ++i) {
     if (!isPlainValue(parameterTypes[i], inverseMode)) return false;
   }
-  if (!isPlainValue(signature.returnType, mode)) return false;
   return true;
 }
 
diff --git a/tests/compiler/bindings/esm.debug.d.ts b/tests/compiler/bindings/esm.debug.d.ts
index a9d795fee1..cbf52b0406 100644
--- a/tests/compiler/bindings/esm.debug.d.ts
+++ b/tests/compiler/bindings/esm.debug.d.ts
@@ -52,6 +52,16 @@ export declare function plainFunction(a: number, b: number): number;
  * @returns `i64`
  */
 export declare function plainFunction64(a: bigint, b: bigint): bigint;
+/**
+ * bindings/esm/getMaxUnsigned32
+ * @returns `u32`
+ */
+export declare function getMaxUnsigned32(): number;
+/**
+ * bindings/esm/getMaxUnsigned64
+ * @returns `u64`
+ */
+export declare function getMaxUnsigned64(): bigint;
 /**
  * bindings/esm/bufferFunction
  * @param a `~lib/arraybuffer/ArrayBuffer`
diff --git a/tests/compiler/bindings/esm.debug.js b/tests/compiler/bindings/esm.debug.js
index ad6cfd1467..21ebe81e62 100644
--- a/tests/compiler/bindings/esm.debug.js
+++ b/tests/compiler/bindings/esm.debug.js
@@ -86,6 +86,14 @@ async function instantiate(module, imports = {}) {
       b = b || 0n;
       return exports.plainFunction64(a, b);
     },
+    getMaxUnsigned32() {
+      // bindings/esm/getMaxUnsigned32() => u32
+      return exports.getMaxUnsigned32() >>> 0;
+    },
+    getMaxUnsigned64() {
+      // bindings/esm/getMaxUnsigned64() => u64
+      return BigInt.asUintN(64, exports.getMaxUnsigned64());
+    },
     bufferFunction(a, b) {
       // bindings/esm/bufferFunction(~lib/arraybuffer/ArrayBuffer, ~lib/arraybuffer/ArrayBuffer) => ~lib/arraybuffer/ArrayBuffer
       a = __retain(__lowerBuffer(a) || __notnull());
@@ -360,6 +368,8 @@ export const {
   ConstEnum,
   plainFunction,
   plainFunction64,
+  getMaxUnsigned32,
+  getMaxUnsigned64,
   bufferFunction,
   stringFunction,
   stringFunctionOptional,
diff --git a/tests/compiler/bindings/esm.debug.wat b/tests/compiler/bindings/esm.debug.wat
index e811a94fe6..f045953ecc 100644
--- a/tests/compiler/bindings/esm.debug.wat
+++ b/tests/compiler/bindings/esm.debug.wat
@@ -12,6 +12,7 @@
  (type $i32_i32_f64_f64_f64_f64_f64_=>_none (func (param i32 i32 f64 f64 f64 f64 f64)))
  (type $f64_=>_f64 (func (param f64) (result f64)))
  (type $i64_i64_=>_i64 (func (param i64 i64) (result i64)))
+ (type $none_=>_i64 (func (result i64)))
  (type $i32_i32_i64_=>_none (func (param i32 i32 i64)))
  (type $i32_i32_=>_f32 (func (param i32 i32) (result f32)))
  (type $i32_f32_=>_none (func (param i32 f32)))
@@ -34,6 +35,8 @@
  (global $bindings/esm/ConstEnum.ONE i32 (i32.const 1))
  (global $bindings/esm/ConstEnum.TWO i32 (i32.const 2))
  (global $bindings/esm/ConstEnum.THREE i32 (i32.const 3))
+ (global $~lib/builtins/u32.MAX_VALUE i32 (i32.const -1))
+ (global $~lib/builtins/u64.MAX_VALUE i64 (i64.const -1))
  (global $~lib/shared/runtime/Runtime.Stub i32 (i32.const 0))
  (global $~lib/shared/runtime/Runtime.Minimal i32 (i32.const 1))
  (global $~lib/shared/runtime/Runtime.Incremental i32 (i32.const 2))
@@ -91,6 +94,8 @@
  (export "ConstEnum.THREE" (global $bindings/esm/ConstEnum.THREE))
  (export "plainFunction" (func $bindings/esm/plainFunction))
  (export "plainFunction64" (func $bindings/esm/plainFunction64))
+ (export "getMaxUnsigned32" (func $bindings/esm/getMaxUnsigned32))
+ (export "getMaxUnsigned64" (func $bindings/esm/getMaxUnsigned64))
  (export "newInternref" (func $bindings/esm/newInternref))
  (export "__new" (func $~lib/rt/itcms/__new))
  (export "__pin" (func $~lib/rt/itcms/__pin))
@@ -118,6 +123,12 @@
   local.get $1
   i64.add
  )
+ (func $bindings/esm/getMaxUnsigned32 (result i32)
+  global.get $~lib/builtins/u32.MAX_VALUE
+ )
+ (func $bindings/esm/getMaxUnsigned64 (result i64)
+  global.get $~lib/builtins/u64.MAX_VALUE
+ )
  (func $~lib/arraybuffer/ArrayBuffer#get:byteLength (param $0 i32) (result i32)
   local.get $0
   i32.const 20
diff --git a/tests/compiler/bindings/esm.js b/tests/compiler/bindings/esm.js
index b279d8e09d..63c6fc8792 100644
--- a/tests/compiler/bindings/esm.js
+++ b/tests/compiler/bindings/esm.js
@@ -35,6 +35,9 @@ export async function postInstantiate(instance) {
   assert.strictEqual(exports.Enum.TWO, 2);
   assert.strictEqual(exports.Enum[2], "TWO");
 
+  assert.strictEqual(exports.getMaxUnsigned32(), 4294967295);
+  assert.strictEqual(exports.getMaxUnsigned64(), 18446744073709551615n);
+
   assert.strictEqual(exports.plainFunction(1, 2), 3);
 
   {
diff --git a/tests/compiler/bindings/esm.release.d.ts b/tests/compiler/bindings/esm.release.d.ts
index a9d795fee1..cbf52b0406 100644
--- a/tests/compiler/bindings/esm.release.d.ts
+++ b/tests/compiler/bindings/esm.release.d.ts
@@ -52,6 +52,16 @@ export declare function plainFunction(a: number, b: number): number;
  * @returns `i64`
  */
 export declare function plainFunction64(a: bigint, b: bigint): bigint;
+/**
+ * bindings/esm/getMaxUnsigned32
+ * @returns `u32`
+ */
+export declare function getMaxUnsigned32(): number;
+/**
+ * bindings/esm/getMaxUnsigned64
+ * @returns `u64`
+ */
+export declare function getMaxUnsigned64(): bigint;
 /**
  * bindings/esm/bufferFunction
  * @param a `~lib/arraybuffer/ArrayBuffer`
diff --git a/tests/compiler/bindings/esm.release.js b/tests/compiler/bindings/esm.release.js
index f2b51c2895..8285c32a1c 100644
--- a/tests/compiler/bindings/esm.release.js
+++ b/tests/compiler/bindings/esm.release.js
@@ -86,6 +86,14 @@ async function instantiate(module, imports = {}) {
       b = b || 0n;
       return exports.plainFunction64(a, b);
     },
+    getMaxUnsigned32() {
+      // bindings/esm/getMaxUnsigned32() => u32
+      return exports.getMaxUnsigned32() >>> 0;
+    },
+    getMaxUnsigned64() {
+      // bindings/esm/getMaxUnsigned64() => u64
+      return BigInt.asUintN(64, exports.getMaxUnsigned64());
+    },
     bufferFunction(a, b) {
       // bindings/esm/bufferFunction(~lib/arraybuffer/ArrayBuffer, ~lib/arraybuffer/ArrayBuffer) => ~lib/arraybuffer/ArrayBuffer
       a = __retain(__lowerBuffer(a) || __notnull());
@@ -360,6 +368,8 @@ export const {
   ConstEnum,
   plainFunction,
   plainFunction64,
+  getMaxUnsigned32,
+  getMaxUnsigned64,
   bufferFunction,
   stringFunction,
   stringFunctionOptional,
diff --git a/tests/compiler/bindings/esm.release.wat b/tests/compiler/bindings/esm.release.wat
index 333923028d..76483b93d9 100644
--- a/tests/compiler/bindings/esm.release.wat
+++ b/tests/compiler/bindings/esm.release.wat
@@ -1,13 +1,14 @@
 (module
  (type $i32_i32_=>_i32 (func (param i32 i32) (result i32)))
  (type $i32_=>_none (func (param i32)))
- (type $none_=>_none (func))
  (type $none_=>_i32 (func (result i32)))
+ (type $none_=>_none (func))
  (type $i32_i32_=>_none (func (param i32 i32)))
  (type $i32_i32_i32_=>_none (func (param i32 i32 i32)))
  (type $i32_i32_f64_f64_f64_f64_f64_=>_none (func (param i32 i32 f64 f64 f64 f64 f64)))
  (type $f64_=>_f64 (func (param f64) (result f64)))
  (type $i64_i64_=>_i64 (func (param i64 i64) (result i64)))
+ (type $none_=>_i64 (func (result i64)))
  (type $i32_i32_i32_i32_=>_none (func (param i32 i32 i32 i32)))
  (type $i32_i32_i64_=>_none (func (param i32 i32 i64)))
  (type $i32_=>_i32 (func (param i32) (result i32)))
@@ -91,6 +92,8 @@
  (export "ConstEnum.THREE" (global $bindings/esm/ConstEnum.THREE))
  (export "plainFunction" (func $bindings/esm/plainFunction))
  (export "plainFunction64" (func $bindings/esm/plainFunction64))
+ (export "getMaxUnsigned32" (func $bindings/esm/getMaxUnsigned32))
+ (export "getMaxUnsigned64" (func $bindings/esm/getMaxUnsigned64))
  (export "newInternref" (func $bindings/esm/newInternref))
  (export "__new" (func $~lib/rt/itcms/__new))
  (export "__pin" (func $~lib/rt/itcms/__pin))
@@ -118,6 +121,12 @@
   local.get $1
   i64.add
  )
+ (func $bindings/esm/getMaxUnsigned32 (result i32)
+  i32.const -1
+ )
+ (func $bindings/esm/getMaxUnsigned64 (result i64)
+  i64.const -1
+ )
  (func $~lib/rt/itcms/visitRoots
   (local $0 i32)
   (local $1 i32)
diff --git a/tests/compiler/bindings/esm.ts b/tests/compiler/bindings/esm.ts
index 944e35d859..3a000c534a 100644
--- a/tests/compiler/bindings/esm.ts
+++ b/tests/compiler/bindings/esm.ts
@@ -26,6 +26,14 @@ export function plainFunction64(a: i64, b: i64): i64 {
   return a + b;
 }
 
+export function getMaxUnsigned32(): u32 {
+  return u32.MAX_VALUE; // 4294967295
+}
+
+export function getMaxUnsigned64(): u64 {
+  return u64.MAX_VALUE; // 18446744073709551615
+}
+
 export function bufferFunction(a: ArrayBuffer, b: ArrayBuffer): ArrayBuffer {
   var aByteLength = a.byteLength;
   var bByteLength = b.byteLength;
diff --git a/tests/compiler/bindings/raw.debug.d.ts b/tests/compiler/bindings/raw.debug.d.ts
index 14bc6d53ec..15e2360189 100644
--- a/tests/compiler/bindings/raw.debug.d.ts
+++ b/tests/compiler/bindings/raw.debug.d.ts
@@ -53,6 +53,16 @@ declare namespace __AdaptedExports {
    * @returns `i64`
    */
   export function plainFunction64(a: bigint, b: bigint): bigint;
+  /**
+   * bindings/esm/getMaxUnsigned32
+   * @returns `u32`
+   */
+  export function getMaxUnsigned32(): number;
+  /**
+   * bindings/esm/getMaxUnsigned64
+   * @returns `u64`
+   */
+  export function getMaxUnsigned64(): bigint;
   /**
    * bindings/esm/bufferFunction
    * @param a `~lib/arraybuffer/ArrayBuffer`
diff --git a/tests/compiler/bindings/raw.debug.js b/tests/compiler/bindings/raw.debug.js
index dabcb032b9..1091069c5b 100644
--- a/tests/compiler/bindings/raw.debug.js
+++ b/tests/compiler/bindings/raw.debug.js
@@ -86,6 +86,14 @@ export async function instantiate(module, imports = {}) {
       b = b || 0n;
       return exports.plainFunction64(a, b);
     },
+    getMaxUnsigned32() {
+      // bindings/esm/getMaxUnsigned32() => u32
+      return exports.getMaxUnsigned32() >>> 0;
+    },
+    getMaxUnsigned64() {
+      // bindings/esm/getMaxUnsigned64() => u64
+      return BigInt.asUintN(64, exports.getMaxUnsigned64());
+    },
     bufferFunction(a, b) {
       // bindings/esm/bufferFunction(~lib/arraybuffer/ArrayBuffer, ~lib/arraybuffer/ArrayBuffer) => ~lib/arraybuffer/ArrayBuffer
       a = __retain(__lowerBuffer(a) || __notnull());
diff --git a/tests/compiler/bindings/raw.debug.wat b/tests/compiler/bindings/raw.debug.wat
index f987fcf6b2..863c18d4e5 100644
--- a/tests/compiler/bindings/raw.debug.wat
+++ b/tests/compiler/bindings/raw.debug.wat
@@ -12,6 +12,7 @@
  (type $i32_i32_f64_f64_f64_f64_f64_=>_none (func (param i32 i32 f64 f64 f64 f64 f64)))
  (type $f64_=>_f64 (func (param f64) (result f64)))
  (type $i64_i64_=>_i64 (func (param i64 i64) (result i64)))
+ (type $none_=>_i64 (func (result i64)))
  (type $i32_i32_i64_=>_none (func (param i32 i32 i64)))
  (type $i32_i32_=>_f32 (func (param i32 i32) (result f32)))
  (type $i32_f32_=>_none (func (param i32 f32)))
@@ -34,6 +35,8 @@
  (global $bindings/esm/ConstEnum.ONE i32 (i32.const 1))
  (global $bindings/esm/ConstEnum.TWO i32 (i32.const 2))
  (global $bindings/esm/ConstEnum.THREE i32 (i32.const 3))
+ (global $~lib/builtins/u32.MAX_VALUE i32 (i32.const -1))
+ (global $~lib/builtins/u64.MAX_VALUE i64 (i64.const -1))
  (global $~lib/shared/runtime/Runtime.Stub i32 (i32.const 0))
  (global $~lib/shared/runtime/Runtime.Minimal i32 (i32.const 1))
  (global $~lib/shared/runtime/Runtime.Incremental i32 (i32.const 2))
@@ -91,6 +94,8 @@
  (export "ConstEnum.THREE" (global $bindings/esm/ConstEnum.THREE))
  (export "plainFunction" (func $bindings/esm/plainFunction))
  (export "plainFunction64" (func $bindings/esm/plainFunction64))
+ (export "getMaxUnsigned32" (func $bindings/esm/getMaxUnsigned32))
+ (export "getMaxUnsigned64" (func $bindings/esm/getMaxUnsigned64))
  (export "newInternref" (func $bindings/esm/newInternref))
  (export "__new" (func $~lib/rt/itcms/__new))
  (export "__pin" (func $~lib/rt/itcms/__pin))
@@ -121,6 +126,12 @@
   local.get $1
   i64.add
  )
+ (func $bindings/esm/getMaxUnsigned32 (result i32)
+  global.get $~lib/builtins/u32.MAX_VALUE
+ )
+ (func $bindings/esm/getMaxUnsigned64 (result i64)
+  global.get $~lib/builtins/u64.MAX_VALUE
+ )
  (func $~lib/arraybuffer/ArrayBuffer#get:byteLength (param $0 i32) (result i32)
   local.get $0
   i32.const 20
diff --git a/tests/compiler/bindings/raw.release.d.ts b/tests/compiler/bindings/raw.release.d.ts
index 14bc6d53ec..15e2360189 100644
--- a/tests/compiler/bindings/raw.release.d.ts
+++ b/tests/compiler/bindings/raw.release.d.ts
@@ -53,6 +53,16 @@ declare namespace __AdaptedExports {
    * @returns `i64`
    */
   export function plainFunction64(a: bigint, b: bigint): bigint;
+  /**
+   * bindings/esm/getMaxUnsigned32
+   * @returns `u32`
+   */
+  export function getMaxUnsigned32(): number;
+  /**
+   * bindings/esm/getMaxUnsigned64
+   * @returns `u64`
+   */
+  export function getMaxUnsigned64(): bigint;
   /**
    * bindings/esm/bufferFunction
    * @param a `~lib/arraybuffer/ArrayBuffer`
diff --git a/tests/compiler/bindings/raw.release.js b/tests/compiler/bindings/raw.release.js
index dabcb032b9..1091069c5b 100644
--- a/tests/compiler/bindings/raw.release.js
+++ b/tests/compiler/bindings/raw.release.js
@@ -86,6 +86,14 @@ export async function instantiate(module, imports = {}) {
       b = b || 0n;
       return exports.plainFunction64(a, b);
     },
+    getMaxUnsigned32() {
+      // bindings/esm/getMaxUnsigned32() => u32
+      return exports.getMaxUnsigned32() >>> 0;
+    },
+    getMaxUnsigned64() {
+      // bindings/esm/getMaxUnsigned64() => u64
+      return BigInt.asUintN(64, exports.getMaxUnsigned64());
+    },
     bufferFunction(a, b) {
       // bindings/esm/bufferFunction(~lib/arraybuffer/ArrayBuffer, ~lib/arraybuffer/ArrayBuffer) => ~lib/arraybuffer/ArrayBuffer
       a = __retain(__lowerBuffer(a) || __notnull());
diff --git a/tests/compiler/bindings/raw.release.wat b/tests/compiler/bindings/raw.release.wat
index f5f70ccc7a..b4c9560f48 100644
--- a/tests/compiler/bindings/raw.release.wat
+++ b/tests/compiler/bindings/raw.release.wat
@@ -1,13 +1,14 @@
 (module
  (type $i32_i32_=>_i32 (func (param i32 i32) (result i32)))
  (type $i32_=>_none (func (param i32)))
- (type $none_=>_none (func))
  (type $none_=>_i32 (func (result i32)))
+ (type $none_=>_none (func))
  (type $i32_i32_=>_none (func (param i32 i32)))
  (type $i32_i32_i32_=>_none (func (param i32 i32 i32)))
  (type $i32_i32_f64_f64_f64_f64_f64_=>_none (func (param i32 i32 f64 f64 f64 f64 f64)))
  (type $f64_=>_f64 (func (param f64) (result f64)))
  (type $i64_i64_=>_i64 (func (param i64 i64) (result i64)))
+ (type $none_=>_i64 (func (result i64)))
  (type $i32_i32_i32_i32_=>_none (func (param i32 i32 i32 i32)))
  (type $i32_i32_i64_=>_none (func (param i32 i32 i64)))
  (type $i32_=>_i32 (func (param i32) (result i32)))
@@ -91,6 +92,8 @@
  (export "ConstEnum.THREE" (global $bindings/esm/ConstEnum.THREE))
  (export "plainFunction" (func $bindings/esm/plainFunction))
  (export "plainFunction64" (func $bindings/esm/plainFunction64))
+ (export "getMaxUnsigned32" (func $bindings/esm/getMaxUnsigned32))
+ (export "getMaxUnsigned64" (func $bindings/esm/getMaxUnsigned64))
  (export "newInternref" (func $bindings/esm/newInternref))
  (export "__new" (func $~lib/rt/itcms/__new))
  (export "__pin" (func $~lib/rt/itcms/__pin))
@@ -118,6 +121,12 @@
   local.get $1
   i64.add
  )
+ (func $bindings/esm/getMaxUnsigned32 (result i32)
+  i32.const -1
+ )
+ (func $bindings/esm/getMaxUnsigned64 (result i64)
+  i64.const -1
+ )
  (func $~lib/rt/itcms/visitRoots
   (local $0 i32)
   (local $1 i32)