diff --git a/crates/cli-support/src/js/binding.rs b/crates/cli-support/src/js/binding.rs
index 637c3a5edf7..91ae75f1103 100644
--- a/crates/cli-support/src/js/binding.rs
+++ b/crates/cli-support/src/js/binding.rs
@@ -575,6 +575,29 @@ impl<'a, 'b> JsBuilder<'a, 'b> {
         ));
     }
 
+    /// The given value is a number (`typeof val === 'number'`), it is
+    /// converted to a bigint. If the value is anything else, it will be
+    /// returned as is.
+    ///
+    /// If the number is not an integer, it will be truncated to an integer.
+    /// If the number is NaN, +Infinity, or -Infinity, the conversion will fail
+    /// and result in a runtime JS `RangeError`.
+    ///
+    /// The returned string the name of a variable that holds the converted
+    /// value.
+    fn number_to_bigint(&mut self, val: &str) -> String {
+        // This conversion relies on the WebAssembly API for correctness. The
+        // API automatically adjusts bigint values that are out of range, so we
+        // just have to pass it any bigint. We truncate the number to an integer
+        // to be consistent with the truncation the WebAssembly API does for
+        // 32-bit integers.
+        let new_var = format!("bigint{}", self.tmp());
+        self.prelude(&format!(
+            "const {new_var} = typeof {val} === 'number' ? BigInt(Math.trunc({val})) : {val};"
+        ));
+        new_var
+    }
+
     fn string_to_memory(
         &mut self,
         mem: walrus::MemoryId,
@@ -731,7 +754,12 @@ fn instruction(
         }
 
         Instruction::Int64ToWasm => {
-            let val = js.pop();
+            let mut val = js.pop();
+            // Regular JS numbers are commonly used for integers >32 bits,
+            // because they can represent integers up to 2^53 exactly. To
+            // support this, we allow both number and bigint for 64-bit
+            // integers.
+            val = js.number_to_bigint(&val);
             js.assert_bigint(&val);
             js.push(val);
         }
@@ -1034,9 +1062,11 @@ fn instruction(
         }
 
         Instruction::FromOptionNative { ty } => {
-            let val = js.pop();
+            let mut val = js.pop();
             js.cx.expose_is_like_none();
             if *ty == ValType::I64 {
+                // same as for Instruction::IntToWasm
+                val = js.number_to_bigint(&val);
                 js.assert_optional_bigint(&val);
             } else {
                 js.assert_optional_number(&val);
@@ -1576,9 +1606,11 @@ fn adapter2ts(
         | AdapterType::NonNull => dst.push_str("number"),
         AdapterType::I64
         | AdapterType::S64
-        | AdapterType::U64
-        | AdapterType::S128
-        | AdapterType::U128 => dst.push_str("bigint"),
+        | AdapterType::U64 => dst.push_str(match position {
+            TypePosition::Argument => "bigint | number",
+            TypePosition::Return => "bigint",
+        }),
+        AdapterType::S128 | AdapterType::U128 => dst.push_str("bigint"),
         AdapterType::String => dst.push_str("string"),
         AdapterType::Externref => dst.push_str("any"),
         AdapterType::Bool => dst.push_str("boolean"),
diff --git a/crates/cli/tests/reference/add.d.ts b/crates/cli/tests/reference/add.d.ts
index f11140413c4..8aa1b2c8d94 100644
--- a/crates/cli/tests/reference/add.d.ts
+++ b/crates/cli/tests/reference/add.d.ts
@@ -2,3 +2,7 @@
 /* eslint-disable */
 export function add_u32(a: number, b: number): number;
 export function add_i32(a: number, b: number): number;
+export function add_u64(a: bigint | number, b: bigint | number): bigint;
+export function add_i64(a: bigint | number, b: bigint | number): bigint;
+export function add_option_u64(a: bigint | number | null | undefined, b: bigint | number): bigint | undefined;
+export function add_option_i64(a: bigint | number | null | undefined, b: bigint | number): bigint | undefined;
diff --git a/crates/cli/tests/reference/add.js b/crates/cli/tests/reference/add.js
index f11b75ef83a..a17a6f390f9 100644
--- a/crates/cli/tests/reference/add.js
+++ b/crates/cli/tests/reference/add.js
@@ -23,6 +23,57 @@ export function add_i32(a, b) {
     return ret;
 }
 
+/**
+ * @param {bigint | number} a
+ * @param {bigint | number} b
+ * @returns {bigint}
+ */
+export function add_u64(a, b) {
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const bigint1 = typeof b === 'number' ? BigInt(Math.trunc(b)) : b;
+    const ret = wasm.add_u64(bigint0, bigint1);
+    return BigInt.asUintN(64, ret);
+}
+
+/**
+ * @param {bigint | number} a
+ * @param {bigint | number} b
+ * @returns {bigint}
+ */
+export function add_i64(a, b) {
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const bigint1 = typeof b === 'number' ? BigInt(Math.trunc(b)) : b;
+    const ret = wasm.add_i64(bigint0, bigint1);
+    return ret;
+}
+
+function isLikeNone(x) {
+    return x === undefined || x === null;
+}
+/**
+ * @param {bigint | number | null | undefined} a
+ * @param {bigint | number} b
+ * @returns {bigint | undefined}
+ */
+export function add_option_u64(a, b) {
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const bigint1 = typeof b === 'number' ? BigInt(Math.trunc(b)) : b;
+    const ret = wasm.add_option_u64(!isLikeNone(bigint0), isLikeNone(bigint0) ? BigInt(0) : bigint0, bigint1);
+    return ret[0] === 0 ? undefined : BigInt.asUintN(64, ret[1]);
+}
+
+/**
+ * @param {bigint | number | null | undefined} a
+ * @param {bigint | number} b
+ * @returns {bigint | undefined}
+ */
+export function add_option_i64(a, b) {
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const bigint1 = typeof b === 'number' ? BigInt(Math.trunc(b)) : b;
+    const ret = wasm.add_option_i64(!isLikeNone(bigint0), isLikeNone(bigint0) ? BigInt(0) : bigint0, bigint1);
+    return ret[0] === 0 ? undefined : ret[1];
+}
+
 export function __wbindgen_init_externref_table() {
     const table = wasm.__wbindgen_export_0;
     const offset = table.grow(4);
diff --git a/crates/cli/tests/reference/add.rs b/crates/cli/tests/reference/add.rs
index f2cc3e7a05f..0b382cb8f28 100644
--- a/crates/cli/tests/reference/add.rs
+++ b/crates/cli/tests/reference/add.rs
@@ -9,3 +9,23 @@ pub fn add_u32(a: u32, b: u32) -> u32 {
 pub fn add_i32(a: i32, b: i32) -> i32 {
     a + b
 }
+
+#[wasm_bindgen]
+pub fn add_u64(a: u64, b: u64) -> u64 {
+    a + b
+}
+
+#[wasm_bindgen]
+pub fn add_i64(a: i64, b: i64) -> i64 {
+    a + b
+}
+
+#[wasm_bindgen]
+pub fn add_option_u64(a: Option<u64>, b: u64) -> Option<u64> {
+    a.map(|a| a + b)
+}
+
+#[wasm_bindgen]
+pub fn add_option_i64(a: Option<i64>, b: i64) -> Option<i64> {
+    a.map(|a| a + b)
+}
diff --git a/crates/cli/tests/reference/add.wat b/crates/cli/tests/reference/add.wat
index bc5cbff68cd..964ef276593 100644
--- a/crates/cli/tests/reference/add.wat
+++ b/crates/cli/tests/reference/add.wat
@@ -1,14 +1,24 @@
 (module $reference_test.wasm
   (type (;0;) (func))
   (type (;1;) (func (param i32 i32) (result i32)))
+  (type (;2;) (func (param i32 i64 i64) (result i32 i64)))
+  (type (;3;) (func (param i64 i64) (result i64)))
   (import "./reference_test_bg.js" "__wbindgen_init_externref_table" (func (;0;) (type 0)))
   (func $add_u32 (;1;) (type 1) (param i32 i32) (result i32))
   (func $add_i32 (;2;) (type 1) (param i32 i32) (result i32))
+  (func $add_u64 (;3;) (type 3) (param i64 i64) (result i64))
+  (func $add_i64 (;4;) (type 3) (param i64 i64) (result i64))
+  (func $"add_option_u64 multivalue shim" (;5;) (type 2) (param i32 i64 i64) (result i32 i64))
+  (func $"add_option_i64 multivalue shim" (;6;) (type 2) (param i32 i64 i64) (result i32 i64))
   (table (;0;) 128 externref)
   (memory (;0;) 17)
   (export "memory" (memory 0))
   (export "add_u32" (func $add_u32))
   (export "add_i32" (func $add_i32))
+  (export "add_u64" (func $add_u64))
+  (export "add_i64" (func $add_i64))
+  (export "add_option_u64" (func $"add_option_u64 multivalue shim"))
+  (export "add_option_i64" (func $"add_option_i64 multivalue shim"))
   (export "__wbindgen_export_0" (table 0))
   (export "__wbindgen_start" (func 0))
   (@custom "target_features" (after code) "\04+\0amultivalue+\0fmutable-globals+\0freference-types+\08sign-ext")
diff --git a/crates/cli/tests/reference/date.d.ts b/crates/cli/tests/reference/date.d.ts
new file mode 100644
index 00000000000..ab20322f079
--- /dev/null
+++ b/crates/cli/tests/reference/date.d.ts
@@ -0,0 +1,3 @@
+/* tslint:disable */
+/* eslint-disable */
+export function date_now(): bigint;
diff --git a/crates/cli/tests/reference/date.js b/crates/cli/tests/reference/date.js
new file mode 100644
index 00000000000..95da99c8617
--- /dev/null
+++ b/crates/cli/tests/reference/date.js
@@ -0,0 +1,30 @@
+let wasm;
+export function __wbg_set_wasm(val) {
+    wasm = val;
+}
+
+/**
+ * @returns {bigint}
+ */
+export function date_now() {
+    const ret = wasm.date_now();
+    return BigInt.asUintN(64, ret);
+}
+
+export function __wbg_now_179748341dc011f4() {
+    const ret = Date.now();
+    const bigint1 = typeof ret === 'number' ? BigInt(Math.trunc(ret)) : ret;
+    return bigint1;
+};
+
+export function __wbindgen_init_externref_table() {
+    const table = wasm.__wbindgen_export_0;
+    const offset = table.grow(4);
+    table.set(0, undefined);
+    table.set(offset + 0, undefined);
+    table.set(offset + 1, null);
+    table.set(offset + 2, true);
+    table.set(offset + 3, false);
+    ;
+};
+
diff --git a/crates/cli/tests/reference/date.rs b/crates/cli/tests/reference/date.rs
new file mode 100644
index 00000000000..3cafddd3d56
--- /dev/null
+++ b/crates/cli/tests/reference/date.rs
@@ -0,0 +1,14 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern "C" {
+    pub type Date;
+
+    #[wasm_bindgen(static_method_of = Date)]
+    pub fn now() -> u64;
+}
+
+#[wasm_bindgen]
+pub fn date_now() -> u64 {
+    Date::now()
+}
diff --git a/crates/cli/tests/reference/date.wat b/crates/cli/tests/reference/date.wat
new file mode 100644
index 00000000000..e4e4701b78d
--- /dev/null
+++ b/crates/cli/tests/reference/date.wat
@@ -0,0 +1,14 @@
+(module $reference_test.wasm
+  (type (;0;) (func))
+  (type (;1;) (func (result i64)))
+  (import "./reference_test_bg.js" "__wbindgen_init_externref_table" (func (;0;) (type 0)))
+  (func $date_now (;1;) (type 1) (result i64))
+  (table (;0;) 128 externref)
+  (memory (;0;) 17)
+  (export "memory" (memory 0))
+  (export "date_now" (func $date_now))
+  (export "__wbindgen_export_0" (table 0))
+  (export "__wbindgen_start" (func 0))
+  (@custom "target_features" (after code) "\04+\0amultivalue+\0fmutable-globals+\0freference-types+\08sign-ext")
+)
+
diff --git a/crates/cli/tests/reference/echo.d.ts b/crates/cli/tests/reference/echo.d.ts
index 61fd4a7925e..f6705cda259 100644
--- a/crates/cli/tests/reference/echo.d.ts
+++ b/crates/cli/tests/reference/echo.d.ts
@@ -6,8 +6,8 @@ export function echo_u16(a: number): number;
 export function echo_i16(a: number): number;
 export function echo_u32(a: number): number;
 export function echo_i32(a: number): number;
-export function echo_u64(a: bigint): bigint;
-export function echo_i64(a: bigint): bigint;
+export function echo_u64(a: bigint | number): bigint;
+export function echo_i64(a: bigint | number): bigint;
 export function echo_u128(a: bigint): bigint;
 export function echo_i128(a: bigint): bigint;
 export function echo_usize(a: number): number;
@@ -42,8 +42,8 @@ export function echo_option_u16(a?: number | null): number | undefined;
 export function echo_option_i16(a?: number | null): number | undefined;
 export function echo_option_u32(a?: number | null): number | undefined;
 export function echo_option_i32(a?: number | null): number | undefined;
-export function echo_option_u64(a?: bigint | null): bigint | undefined;
-export function echo_option_i64(a?: bigint | null): bigint | undefined;
+export function echo_option_u64(a?: bigint | number | null): bigint | undefined;
+export function echo_option_i64(a?: bigint | number | null): bigint | undefined;
 export function echo_option_u128(a?: bigint | null): bigint | undefined;
 export function echo_option_i128(a?: bigint | null): bigint | undefined;
 export function echo_option_usize(a?: number | null): number | undefined;
diff --git a/crates/cli/tests/reference/echo.js b/crates/cli/tests/reference/echo.js
index c3e9c47f835..4879b1cd3ea 100644
--- a/crates/cli/tests/reference/echo.js
+++ b/crates/cli/tests/reference/echo.js
@@ -214,20 +214,22 @@ export function echo_i32(a) {
 }
 
 /**
- * @param {bigint} a
+ * @param {bigint | number} a
  * @returns {bigint}
  */
 export function echo_u64(a) {
-    const ret = wasm.echo_u64(a);
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const ret = wasm.echo_u64(bigint0);
     return BigInt.asUintN(64, ret);
 }
 
 /**
- * @param {bigint} a
+ * @param {bigint | number} a
  * @returns {bigint}
  */
 export function echo_i64(a) {
-    const ret = wasm.echo_i64(a);
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const ret = wasm.echo_i64(bigint0);
     return ret;
 }
 
@@ -781,20 +783,22 @@ export function echo_option_i32(a) {
 }
 
 /**
- * @param {bigint | null} [a]
+ * @param {bigint | number | null} [a]
  * @returns {bigint | undefined}
  */
 export function echo_option_u64(a) {
-    const ret = wasm.echo_option_u64(!isLikeNone(a), isLikeNone(a) ? BigInt(0) : a);
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const ret = wasm.echo_option_u64(!isLikeNone(bigint0), isLikeNone(bigint0) ? BigInt(0) : bigint0);
     return ret[0] === 0 ? undefined : BigInt.asUintN(64, ret[1]);
 }
 
 /**
- * @param {bigint | null} [a]
+ * @param {bigint | number | null} [a]
  * @returns {bigint | undefined}
  */
 export function echo_option_i64(a) {
-    const ret = wasm.echo_option_i64(!isLikeNone(a), isLikeNone(a) ? BigInt(0) : a);
+    const bigint0 = typeof a === 'number' ? BigInt(Math.trunc(a)) : a;
+    const ret = wasm.echo_option_i64(!isLikeNone(bigint0), isLikeNone(bigint0) ? BigInt(0) : bigint0);
     return ret[0] === 0 ? undefined : ret[1];
 }
 
diff --git a/crates/cli/tests/reference/wasm-export-types.d.ts b/crates/cli/tests/reference/wasm-export-types.d.ts
index a5f399db59d..86c9297d781 100644
--- a/crates/cli/tests/reference/wasm-export-types.d.ts
+++ b/crates/cli/tests/reference/wasm-export-types.d.ts
@@ -1,6 +1,6 @@
 /* tslint:disable */
 /* eslint-disable */
-export function example(a: number, b: bigint, c: any, d: string): string;
+export function example(a: number, b: bigint | number, c: any, d: string): string;
 export function example_128(a: bigint): bigint | undefined;
 
 export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;
diff --git a/crates/cli/tests/reference/wasm-export-types.js b/crates/cli/tests/reference/wasm-export-types.js
index de290e90502..1515cab3f77 100644
--- a/crates/cli/tests/reference/wasm-export-types.js
+++ b/crates/cli/tests/reference/wasm-export-types.js
@@ -75,23 +75,24 @@ function passStringToWasm0(arg, malloc, realloc) {
 }
 /**
  * @param {number} a
- * @param {bigint} b
+ * @param {bigint | number} b
  * @param {any} c
  * @param {string} d
  * @returns {string}
  */
 export function example(a, b, c, d) {
-    let deferred2_0;
-    let deferred2_1;
+    let deferred3_0;
+    let deferred3_1;
     try {
-        const ptr0 = passStringToWasm0(d, wasm.__wbindgen_malloc, wasm.__wbindgen_realloc);
-        const len0 = WASM_VECTOR_LEN;
-        const ret = wasm.example(a, b, c, ptr0, len0);
-        deferred2_0 = ret[0];
-        deferred2_1 = ret[1];
+        const bigint0 = typeof b === 'number' ? BigInt(Math.trunc(b)) : b;
+        const ptr1 = passStringToWasm0(d, wasm.__wbindgen_malloc, wasm.__wbindgen_realloc);
+        const len1 = WASM_VECTOR_LEN;
+        const ret = wasm.example(a, bigint0, c, ptr1, len1);
+        deferred3_0 = ret[0];
+        deferred3_1 = ret[1];
         return getStringFromWasm0(ret[0], ret[1]);
     } finally {
-        wasm.__wbindgen_free(deferred2_0, deferred2_1, 1);
+        wasm.__wbindgen_free(deferred3_0, deferred3_1, 1);
     }
 }
 
diff --git a/tests/wasm/optional_primitives.js b/tests/wasm/optional_primitives.js
index 499dd236d30..8a2243018e6 100644
--- a/tests/wasm/optional_primitives.js
+++ b/tests/wasm/optional_primitives.js
@@ -97,12 +97,23 @@ exports.js_works = () => {
     assert.strictEqual(wasm.optional_i64_identity(wasm.optional_i64_neg_one()), BigInt('-1'));
     assert.strictEqual(wasm.optional_i64_identity(wasm.optional_i64_min()), BigInt('-9223372036854775808'));
     assert.strictEqual(wasm.optional_i64_identity(wasm.optional_i64_max()), BigInt('9223372036854775807'));
+    assert.strictEqual(wasm.optional_i64_identity(0), BigInt('0'));
+    assert.strictEqual(wasm.optional_i64_identity(1.99), BigInt('1'));
+    assert.strictEqual(wasm.optional_i64_identity(-1.99), BigInt('-1'));
+    assert.throws(() => wasm.optional_i64_identity(NaN));
+    assert.throws(() => wasm.optional_i64_identity(Infinity));
 
     assert.strictEqual(wasm.optional_u64_identity(wasm.optional_u64_none()), undefined);
     assert.strictEqual(wasm.optional_u64_identity(wasm.optional_u64_zero()), BigInt('0'));
     assert.strictEqual(wasm.optional_u64_identity(wasm.optional_u64_one()), BigInt('1'));
     assert.strictEqual(wasm.optional_u64_identity(wasm.optional_u64_min()), BigInt('0'));
     assert.strictEqual(wasm.optional_u64_identity(wasm.optional_u64_max()), BigInt('18446744073709551615'));
+    assert.strictEqual(wasm.optional_u64_identity(0), BigInt('0'));
+    assert.strictEqual(wasm.optional_u64_identity(1.99), BigInt('1'));
+    assert.strictEqual(wasm.optional_u64_identity(-1n), BigInt('18446744073709551615')); // because modulo 2^64
+    assert.strictEqual(wasm.optional_u64_identity(-1.99), BigInt('18446744073709551615')); // because modulo 2^64
+    assert.throws(() => wasm.optional_u64_identity(NaN));
+    assert.throws(() => wasm.optional_u64_identity(Infinity));
 
     assert.strictEqual(wasm.optional_i128_identity(wasm.optional_i128_none()), undefined);
     assert.strictEqual(wasm.optional_i128_identity(wasm.optional_i128_zero()), BigInt('0'));