diff --git a/src/json-type-value/Value.ts b/src/json-type-value/Value.ts
index 7e18ae229d..3a66d3e93e 100644
--- a/src/json-type-value/Value.ts
+++ b/src/json-type-value/Value.ts
@@ -16,3 +16,24 @@ export class Value<T extends Type = Type> {
     else type.encoder(codec.format)(value, encoder);
   }
 }
+
+if (process.env.NODE_ENV !== 'production') {
+  const encode = Value.prototype.encode;
+  Value.prototype.encode = function (codec: JsonValueCodec): void {
+    try {
+      encode.call(this, codec);
+    } catch (error) {
+      try {
+        // tslint:disable-next-line no-console
+        console.error(error);
+        const type = this.type;
+        if (type) {
+          const err = type.validator('object')(this.data);
+          // tslint:disable-next-line no-console
+          console.error(err);
+        }
+      } catch {}
+      throw error;
+    }
+  };
+}
diff --git a/src/json-type/system/TypeSystem.ts b/src/json-type/system/TypeSystem.ts
index bf3b9ae239..8e26786a02 100644
--- a/src/json-type/system/TypeSystem.ts
+++ b/src/json-type/system/TypeSystem.ts
@@ -23,14 +23,6 @@ export class TypeSystem implements Printable {
     return alias;
   };
 
-  public importTypes<A extends TypeMap>(
-    types: A,
-  ): {readonly [K in keyof A]: TypeAlias<K extends string ? K : never, A[K]>} {
-    const result = {} as any;
-    for (const id in types) result[id] = this.alias(id, types[id]);
-    return result;
-  }
-
   public readonly unalias = <K extends string>(id: K): TypeAlias<K, Type> => {
     const alias = this.aliases.get(id);
     if (!alias) throw new Error(`Alias [id = ${id}] not found.`);
@@ -66,6 +58,19 @@ export class TypeSystem implements Printable {
     return result;
   }
 
+  public importTypes<A extends TypeMap>(
+    types: A,
+  ): {
+    readonly [K in keyof A]: TypeAlias<
+      K extends string ? K : never,
+      /** @todo Replace `any` by inferred type here. */ any
+    >;
+  } {
+    const result = {} as any;
+    for (const id in types) result[id] = this.alias(id, this.t.import(types[id]));
+    return result;
+  }
+
   public toString(tab: string = '') {
     const nl = () => '';
     return (
diff --git a/src/json-type/type/TypeBuilder.ts b/src/json-type/type/TypeBuilder.ts
index c8857f6bbc..74885ae4e7 100644
--- a/src/json-type/type/TypeBuilder.ts
+++ b/src/json-type/type/TypeBuilder.ts
@@ -178,6 +178,8 @@ export class TypeBuilder {
         return this.Binary(this.import(node.type), node);
       case 'arr':
         return this.Array(this.import(node.type), node);
+      case 'tup':
+        return this.Tuple(...node.types.map((t: schema.Schema) => this.import(t))).options(node);
       case 'obj': {
         return this.Object(
           ...node.fields.map((f: any) =>
@@ -195,6 +197,14 @@ export class TypeBuilder {
         return this.Or(...node.types.map((t) => this.import(t as schema.Schema))).options(node);
       case 'ref':
         return this.Ref(node.ref).options(node);
+      case 'fn':
+        return this.Function(this.import(node.req as schema.Schema), this.import(node.res as schema.Schema)).options(
+          node,
+        );
+      case 'fn$':
+        return this.Function$(this.import(node.req as schema.Schema), this.import(node.res as schema.Schema)).options(
+          node,
+        );
     }
     throw new Error(`UNKNOWN_NODE [${node.kind}]`);
   }
diff --git a/src/json-type/type/types.ts b/src/json-type/type/types.ts
index 77a71f364d..d92c32a70f 100644
--- a/src/json-type/type/types.ts
+++ b/src/json-type/type/types.ts
@@ -35,7 +35,7 @@ export type SchemaOfObjectFieldType<F> =
 
 export type SchemaOfObjectFields<F> = {[K in keyof F]: SchemaOfObjectFieldType<F[K]>};
 
-export type TypeMap = {[name: string]: Type};
+export type TypeMap = {[name: string]: schema.Schema};
 
 export type FilterFunctions<T> = {
   [K in keyof T as T[K] extends classes.FunctionType<any, any>