diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index 9f09098eb..e2dc13427 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -4162,7 +4162,6 @@ class OldTestIntFlag(unittest.TestCase):
         self.assertEqual(str(NoName.ONE & NoName.TWO), 'NoName(0)')
         self.assertEqual(str(NoName(0)), 'NoName(0)')
 
-    @unittest.expectedFailure # TODO: RUSTPYTHON; format(NewPerm.R) does not use __str__
     def test_format(self):
         Perm = self.Perm
         self.assertEqual(format(Perm.R, ''), '4')
diff --git a/crates/vm/src/builtins/complex.rs b/crates/vm/src/builtins/complex.rs
index 78729b2f5..dd6806155 100644
--- a/crates/vm/src/builtins/complex.rs
+++ b/crates/vm/src/builtins/complex.rs
@@ -276,9 +276,13 @@ impl PyComplex {
     }
 
     #[pymethod]
-    fn __format__(&self, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
+    fn __format__(zelf: &Py<Self>, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
+        // Empty format spec: equivalent to str(self)
+        if spec.is_empty() {
+            return Ok(zelf.as_object().str(vm)?.as_str().to_owned());
+        }
         FormatSpec::parse(spec.as_str())
-            .and_then(|format_spec| format_spec.format_complex(&self.value))
+            .and_then(|format_spec| format_spec.format_complex(&zelf.value))
             .map_err(|err| err.into_pyexception(vm))
     }
 }
diff --git a/crates/vm/src/builtins/float.rs b/crates/vm/src/builtins/float.rs
index 9941aea9b..230d288b7 100644
--- a/crates/vm/src/builtins/float.rs
+++ b/crates/vm/src/builtins/float.rs
@@ -214,9 +214,13 @@ fn float_from_string(val: PyObjectRef, vm: &VirtualMachine) -> PyResult<f64> {
 )]
 impl PyFloat {
     #[pymethod]
-    fn __format__(&self, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
+    fn __format__(zelf: &Py<Self>, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
+        // Empty format spec: equivalent to str(self)
+        if spec.is_empty() {
+            return Ok(zelf.as_object().str(vm)?.as_str().to_owned());
+        }
         FormatSpec::parse(spec.as_str())
-            .and_then(|format_spec| format_spec.format_float(self.value))
+            .and_then(|format_spec| format_spec.format_float(zelf.value))
             .map_err(|err| err.into_pyexception(vm))
     }
 
diff --git a/crates/vm/src/builtins/int.rs b/crates/vm/src/builtins/int.rs
index 765f5e245..273199f69 100644
--- a/crates/vm/src/builtins/int.rs
+++ b/crates/vm/src/builtins/int.rs
@@ -444,9 +444,13 @@ impl PyInt {
     }
 
     #[pymethod]
-    fn __format__(&self, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
+    fn __format__(zelf: &Py<Self>, spec: PyStrRef, vm: &VirtualMachine) -> PyResult<String> {
+        // Empty format spec on a subclass: equivalent to str(self)
+        if spec.is_empty() && !zelf.class().is(vm.ctx.types.int_type) {
+            return Ok(zelf.as_object().str(vm)?.as_str().to_owned());
+        }
         FormatSpec::parse(spec.as_str())
-            .and_then(|format_spec| format_spec.format_int(&self.value))
+            .and_then(|format_spec| format_spec.format_int(&zelf.value))
             .map_err(|err| err.into_pyexception(vm))
     }