diff --git a/devs/run-tests/02numbers.ts b/devs/run-tests/02numbers.ts
index a8c93e682d..e26621618e 100644
--- a/devs/run-tests/02numbers.ts
+++ b/devs/run-tests/02numbers.ts
@@ -242,10 +242,15 @@ function testEnumToString() {
     assert(enumTest + "" === "1", "enum tostring in concatenation")
 }
 
+function testToFixed() {
+    const numObj = 12345.6789;
+
+    assert(numObj.toFixed(5) === '12346', 'testToFixed') // '12346'; rounding, no fractional part
+}
+
 testComma()
 testNums()
 testNaN()
 testUnaryPlus()
 testEnumToString()
-
-
+testToFixed()
\ No newline at end of file
diff --git a/packages/core/src/corelib.d.ts b/packages/core/src/corelib.d.ts
index 09a94a2b29..845dd7bc3b 100644
--- a/packages/core/src/corelib.d.ts
+++ b/packages/core/src/corelib.d.ts
@@ -197,7 +197,18 @@ interface StringConstructor {
 declare var String: StringConstructor
 
 interface Boolean {}
-interface Number {}
+
+interface NumberConstructor {
+    readonly prototype: Number
+}
+
+declare var Number: NumberConstructor
+
+interface Number {
+
+    // todo
+    toFixed(digits?: number): string
+}
 
 interface RegExp {}
 interface IterableIterator<T> {}
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 99a878bcdc..8d8b740b2e 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -14,4 +14,5 @@ import "./button"
 import "./magneticfieldlevel"
 import "./buzzer"
 import "./ledstrip"
-import "./gamepad"
\ No newline at end of file
+import "./gamepad"
+import "./number"
\ No newline at end of file
diff --git a/packages/core/src/number.ts b/packages/core/src/number.ts
new file mode 100644
index 0000000000..a8cf82b0d7
--- /dev/null
+++ b/packages/core/src/number.ts
@@ -0,0 +1,3 @@
+Number.prototype.toFixed = function(digits: number = 0): string {
+    return "";
+}
\ No newline at end of file
diff --git a/runtime/devicescript/objects.c b/runtime/devicescript/objects.c
index b75762b7b7..1e80756c70 100644
--- a/runtime/devicescript/objects.c
+++ b/runtime/devicescript/objects.c
@@ -261,8 +261,9 @@ static const uint8_t builtin_proto_idx[] = {
     [DEVS_BUILTIN_OBJECT_BUFFER] = 10,
     [DEVS_BUILTIN_OBJECT_GPIO_PROTOTYPE] = 11,
     [DEVS_BUILTIN_OBJECT_GPIO] = 12,
+    [DEVS_BUILTIN_OBJECT_NUMBER_PROTOTYPE] = 13,
 };
-#define MAX_PROTO 12
+#define MAX_PROTO 13
 
 devs_maplike_t *devs_get_builtin_object(devs_ctx_t *ctx, unsigned idx) {
     if (idx < sizeof(builtin_proto_idx)) {