Truffle/Web3: myContract.method.estimateGas causes BigNumber error

Question

I get the following error when running truffle test:

{ BigNumber Error: new BigNumber() not a number: [object Object]
    at raise (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/node_modules/bignumber.js/bignumber.js:1177:25)
    at /Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/node_modules/bignumber.js/bignumber.js:1165:33
    at new BigNumber (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/node_modules/bignumber.js/bignumber.js:193:67)
    at new BigNumber (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/node_modules/bignumber.js/bignumber.js:203:25)
    at toBigNumber (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/lib/utils/utils.js:367:12)
    at Object.toTwosComplement (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/lib/utils/utils.js:378:21)
    at SolidityTypeUInt.formatInputInt [as _inputFormatter] (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/lib/solidity/formatters.js:40:38)
    at SolidityTypeUInt.SolidityType.encode (/Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/lib/solidity/type.js:188:17)
    at /Users/danielyakobian/.nvm/versions/node/v7.5.0/lib/node_modules/truffle/node_modules/web3/lib/solidity/coder.js:91:29
    at Array.map (native) name: 'BigNumber Error' }

I've narrowed the cause to estimateGas function called in the following code:

        return FlightFuture.deployed()
        .then((instance) => {
            future = instance;
            return future.offer.estimateGas();
        })
        .then((gas) => {
            transaction_options.gas = gas;
            console.log(transaction_options.gas);
            return future.offer.apply(this, valid_offer_params.concat(transaction_options))
        })

Im having trouble finding any documentation on how to call estimateGas on a contract function, any ideas what I'm doing wrong?