diff --git a/tests/snippets/builtin_format.py b/tests/snippets/builtin_format.py
index 039c61121..9465faa65 100644
--- a/tests/snippets/builtin_format.py
+++ b/tests/snippets/builtin_format.py
@@ -12,3 +12,9 @@ class BadFormat:
     def __format__(self, spec):
         return 42
 assert_raises(TypeError, format, BadFormat())
+
+def test_zero_padding():
+    i = 1
+    assert f'{i:04d}' == '0001'
+
+test_zero_padding()
diff --git a/vm/src/format.rs b/vm/src/format.rs
index e76e8c97f..37b737d72 100644
--- a/vm/src/format.rs
+++ b/vm/src/format.rs
@@ -181,11 +181,11 @@ fn parse_alternate_form(text: &str) -> (bool, &str) {
     }
 }
 
-fn parse_zero(text: &str) -> &str {
+fn parse_zero(text: &str) -> (bool, &str) {
     let mut chars = text.chars();
     match chars.next() {
-        Some('0') => chars.as_str(),
-        _ => text,
+        Some('0') => (true, chars.as_str()),
+        _ => (false, text),
     }
 }
 
@@ -235,15 +235,20 @@ fn parse_format_type(text: &str) -> (Option<FormatType>, &str) {
 
 fn parse_format_spec(text: &str) -> FormatSpec {
     let (preconversor, after_preconversor) = parse_preconversor(text);
-    let (fill, align, after_align) = parse_fill_and_align(after_preconversor);
+    let (mut fill, mut align, after_align) = parse_fill_and_align(after_preconversor);
     let (sign, after_sign) = parse_sign(after_align);
     let (alternate_form, after_alternate_form) = parse_alternate_form(after_sign);
-    let after_zero = parse_zero(after_alternate_form);
+    let (zero, after_zero) = parse_zero(after_alternate_form);
     let (width, after_width) = parse_number(after_zero);
     let (grouping_option, after_grouping_option) = parse_grouping_option(after_width);
     let (precision, after_precision) = parse_precision(after_grouping_option);
     let (format_type, _) = parse_format_type(after_precision);
 
+    if zero && fill.is_none() {
+        fill.replace('0');
+        align = align.or(Some(FormatAlign::AfterSign));
+    }
+
     FormatSpec {
         preconversor,
         fill,
diff --git a/vm/src/obj/objstr.rs b/vm/src/obj/objstr.rs
index 4c42de58c..5ff1424f3 100644
--- a/vm/src/obj/objstr.rs
+++ b/vm/src/obj/objstr.rs
@@ -1326,9 +1326,7 @@ fn try_update_quantity_from_tuple(
                         Ok(tuple_index)
                     }
                 }
-                None => {
-                    Err(vm.new_type_error("not enough arguments for format string".to_string()))
-                }
+                None => Err(vm.new_type_error("not enough arguments for format string".to_string())),
             }
         }
         _ => Ok(tuple_index),
diff --git a/vm/src/stdlib/ast.rs b/vm/src/stdlib/ast.rs
index cea1674c4..32986a24c 100644
--- a/vm/src/stdlib/ast.rs
+++ b/vm/src/stdlib/ast.rs
@@ -620,12 +620,8 @@ fn comprehension_to_ast(
 
 fn string_to_ast(vm: &VirtualMachine, string: &ast::StringGroup) -> PyResult<AstNodeRef> {
     let string = match string {
-        ast::StringGroup::Constant { value } => {
-            node!(vm, Str, { s => vm.ctx.new_str(value.clone()) })
-        }
-        ast::StringGroup::FormattedValue { value, .. } => {
-            node!(vm, FormattedValue, { value => expression_to_ast(vm, value)? })
-        }
+        ast::StringGroup::Constant { value } => node!(vm, Str, { s => vm.ctx.new_str(value.clone()) }),
+        ast::StringGroup::FormattedValue { value, .. } => node!(vm, FormattedValue, { value => expression_to_ast(vm, value)? }),
         ast::StringGroup::Joined { values } => {
             let py_values = map_ast(string_to_ast, vm, &values)?;
             node!(vm, JoinedStr, { values => py_values })
diff --git a/vm/src/stdlib/unicodedata.rs b/vm/src/stdlib/unicodedata.rs
index b1e75730b..5c0eeb155 100644
--- a/vm/src/stdlib/unicodedata.rs
+++ b/vm/src/stdlib/unicodedata.rs
@@ -54,9 +54,7 @@ fn name(
     } else {
         match default {
             OptionalArg::Present(obj) => Ok(obj),
-            OptionalArg::Missing => {
-                Err(vm.new_value_error("character name not found!".to_string()))
-            }
+            OptionalArg::Missing => Err(vm.new_value_error("character name not found!".to_string())),
         }
     }
 }
diff --git a/wasm/lib/src/browser_module.rs b/wasm/lib/src/browser_module.rs
index f5878d7fb..9bdf39803 100644
--- a/wasm/lib/src/browser_module.rs
+++ b/wasm/lib/src/browser_module.rs
@@ -137,7 +137,7 @@ fn browser_request_animation_frame(func: PyCallable, vm: &VirtualMachine) -> PyR
 
         let closure = f.borrow_mut().take();
         drop(closure);
-    }) as Box<Fn(f64)>));
+    }) as Box<dyn Fn(f64)>));
 
     let id = window()
         .request_animation_frame(&js_sys::Function::from(