diff --git a/bumpversion/versioning/serialization.py b/bumpversion/versioning/serialization.py
index b119d65..a7c36f4 100644
--- a/bumpversion/versioning/serialization.py
+++ b/bumpversion/versioning/serialization.py
@@ -131,7 +131,30 @@ def serialize(version: Version, serialize_patterns: List[str], context: MutableM
 
     chosen_pattern = sorted_patterns[0]["pattern"]
     logger.debug("Using serialization format '%s'", chosen_pattern)
-    serialized = chosen_pattern.format(**local_context)
+
+    # Handle format specifiers like {:02} for zero-padding
+    # Python's format spec works on integers, but version values are strings
+    # We need to convert them to int when a format spec is present
+    
+    # Extract format specs from the pattern to know which values need int conversion
+    format_specs = {}
+    for field_match in re.finditer(r'\{(\w+)(?::([^}]*))?\}', chosen_pattern):
+        var_name = field_match.group(1)
+        spec = field_match.group(2) if field_match.group(2) else ""
+        if spec:
+            format_specs[var_name] = spec
+    
+    # Convert values with format specs to int
+    serialized_context = dict(local_context)
+    for var_name, spec in format_specs.items():
+        if var_name in serialized_context:
+            try:
+                serialized_context[var_name] = int(serialized_context[var_name])
+            except (ValueError, TypeError):
+                # If conversion fails, keep as string
+                pass
+    
+    serialized = chosen_pattern.format(**serialized_context)
     logger.debug("Serialized to '%s'", serialized)
     logger.dedent()