diff --git a/tests/snippets/builtin_format.py b/tests/snippets/builtin_format.py
index 9465faa65..46b627ad5 100644
--- a/tests/snippets/builtin_format.py
+++ b/tests/snippets/builtin_format.py
@@ -18,3 +18,12 @@ def test_zero_padding():
     assert f'{i:04d}' == '0001'
 
 test_zero_padding()
+
+assert '{:,}'.format(100) == '100'
+assert '{:,}'.format(1024) == '1,024'
+assert '{:_}'.format(65536) == '65_536'
+assert '{:_}'.format(4294967296) == '4_294_967_296'
+assert f'{100:_}' == '100'
+assert f'{1024:_}' == '1_024'
+assert f'{65536:,}' == '65,536'
+assert f'{4294967296:,}' == '4,294,967,296'
diff --git a/vm/src/format.rs b/vm/src/format.rs
index 37b737d72..aaf5f4163 100644
--- a/vm/src/format.rs
+++ b/vm/src/format.rs
@@ -279,15 +279,12 @@ impl FormatSpec {
         separator: char,
     ) -> String {
         let mut result = String::new();
-        let mut remaining: usize = magnitude_string.len() % interval;
-        if remaining == 0 {
-            remaining = interval;
-        }
+        let mut remaining: usize = magnitude_string.len();
         for c in magnitude_string.chars() {
             result.push(c);
-            if remaining == 0 {
+            remaining -= 1;
+            if remaining % interval == 0 && remaining > 0 {
                 result.push(separator);
-                remaining = interval;
             }
         }
         result