diff --git a/package.json b/package.json
index 813b25e..90f1301 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@weiroll/weiroll.js",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "The weiroll planner in JS",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
diff --git a/src/index.ts b/src/index.ts
index e035436..5da8d38 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -6,10 +6,7 @@ export {
     ContractFunction,
     FunctionCall,
     Value,
-    StaticValue,
-    ReturnValue
-} from './contract';
-
-export {
+    LiteralValue,
+    ReturnValue,
     Planner
 } from './planner';
\ No newline at end of file
diff --git a/src/planner.ts b/src/planner.ts
index 10b68df..c87c2de 100644
--- a/src/planner.ts
+++ b/src/planner.ts
@@ -53,6 +53,9 @@ function abiEncodeSingle(param: ParamType, value: any): LiteralValue {
 
 function buildCall(contract: Contract, fragment: FunctionFragment): ContractFunction {
     return function(...args: Array<any>): FunctionCall {
+        if(args.length != fragment.inputs.length) {
+            throw new Error(`Function ${fragment.name} has ${fragment.inputs.length} arguments but ${args.length} provided`);
+        }
         const encodedArgs = args.map((arg, idx) => {
             const param = fragment.inputs[idx];
             if(isReturnValue(arg)) {
diff --git a/tests/test_planner.ts b/tests/test_planner.ts
index 5d5cef3..e62fa41 100644
--- a/tests/test_planner.ts
+++ b/tests/test_planner.ts
@@ -148,4 +148,9 @@ describe('Planner', () => {
         expect(state[0]).to.equal(hexDataSlice(defaultAbiCoder.encode(['string'], ["Hello, "]), 32));
         expect(state[1]).to.equal(hexDataSlice(defaultAbiCoder.encode(['string'], ["world!"]), 32));
     });
+
+    it('requires argument counts to match the function definition', () => {
+        const planner = new Planner();
+        expect(() => planner.addCommand(Math.add(1))).to.throw();
+    })
 });
diff --git a/tsconfig.json b/tsconfig.json
index 694d472..21979fc 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -3,7 +3,7 @@
     "outDir": "./dist/",
     "sourceMap": true,
     "noImplicitAny": true,
-    "module": "es6",
+    "module": "commonjs",
     "target": "es5",
     "jsx": "react",
     "allowJs": true,