diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2475578c..9a94781d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ that can be found in the LICENSE file. -->
 
 # Changelog
 
+## 1.0.0-dev.32
+
+- Make parsable big number string as covariant of Fixed classes.
+
 ## 1.0.0-dev.31
 
 - Treat parsable big number string as a covariant of the `Nat` class.
diff --git a/packages/agent_dart/pubspec.yaml b/packages/agent_dart/pubspec.yaml
index dddacd9f..7058f19e 100644
--- a/packages/agent_dart/pubspec.yaml
+++ b/packages/agent_dart/pubspec.yaml
@@ -1,5 +1,5 @@
 name: agent_dart
-version: 1.0.0-dev.31
+version: 1.0.0-dev.32
 
 description: |
   An agent library built for Internet Computer,
diff --git a/packages/agent_dart_base/lib/candid/idl.dart b/packages/agent_dart_base/lib/candid/idl.dart
index 075845e8..779ce55e 100644
--- a/packages/agent_dart_base/lib/candid/idl.dart
+++ b/packages/agent_dart_base/lib/candid/idl.dart
@@ -636,6 +636,9 @@ class FixedIntClass extends PrimitiveType {
     } else if (x is int) {
       final v = BigInt.from(x);
       return v >= min && v <= max;
+    } else if (x is String && BigInt.tryParse(x) != null) {
+      final v = BigInt.parse(x);
+      return v >= min && v <= max;
     } else {
       return false;
     }
@@ -696,6 +699,11 @@ class FixedNatClass extends PrimitiveType<dynamic> {
     } else if (x is int && x >= 0) {
       final v = BigInt.from(x);
       return v < max;
+    } else if (x is String &&
+        BigInt.tryParse(x) != null &&
+        BigInt.parse(x) >= BigInt.zero) {
+      final v = BigInt.parse(x);
+      return v < max;
     } else {
       return false;
     }
diff --git a/packages/agent_dart_base/pubspec.yaml b/packages/agent_dart_base/pubspec.yaml
index 4bc385d8..7efc1494 100644
--- a/packages/agent_dart_base/pubspec.yaml
+++ b/packages/agent_dart_base/pubspec.yaml
@@ -1,5 +1,5 @@
 name: agent_dart_base
-version: 1.0.0-dev.31
+version: 1.0.0-dev.32
 
 description: The Dart plugin that bridges Rust implementation for agent_dart.
 repository: https://github.com/AstroxNetwork/agent_dart
diff --git a/packages/agent_dart_ffi/pubspec.yaml b/packages/agent_dart_ffi/pubspec.yaml
index cc7c35fb..5401f0af 100644
--- a/packages/agent_dart_ffi/pubspec.yaml
+++ b/packages/agent_dart_ffi/pubspec.yaml
@@ -1,5 +1,5 @@
 name: agent_dart_ffi
-version: 1.0.0-dev.31
+version: 1.0.0-dev.32
 
 description: The FFI plugin that bridges Rust implementation for agent_dart.
 repository: https://github.com/AstroxNetwork/agent_dart