diff --git a/types/genesis_test.go b/types/genesis_test.go
index 7d7731f13..75184e5a6 100644
--- a/types/genesis_test.go
+++ b/types/genesis_test.go
@@ -12,11 +12,12 @@ func TestGenesis(t *testing.T) {
 
 	// test some bad ones from raw json
 	testCases := [][]byte{
-		[]byte{},                                // empty
-		[]byte{1, 1, 1, 1, 1},                   // junk
-		[]byte(`{}`),                            // empty
-		[]byte(`{"chain_id": "mychain"}`),       // missing validators
-		[]byte(`{"validators": [{"data":abcd}`), // missing validators
+		[]byte{},                                             // empty
+		[]byte{1, 1, 1, 1, 1},                                // junk
+		[]byte(`{}`),                                         // empty
+		[]byte(`{"chain_id": "mychain"}`),                    // missing validators
+		[]byte(`{"chain_id": "mychain", "validators": []`),   // missing validators
+		[]byte(`{"chain_id": "mychain", "validators": [{}]`), // missing validators
 		[]byte(`{"validators":[{"pub_key":
 		{"type":"ed25519","data":"961EAB8752E51A03618502F55C2B6E09C38C65635C64CCF3173ED452CF86C957"},
 		"amount":10,"name":""}]}`), // missing chain_id
@@ -24,13 +25,13 @@ func TestGenesis(t *testing.T) {
 
 	for _, testCase := range testCases {
 		_, err := GenesisDocFromJSON(testCase)
-		assert.NotNil(t, err, "expected error for empty genDoc json")
+		assert.Error(t, err, "expected error for empty genDoc json")
 	}
 
 	// test a good one by raw json
 	genDocBytes := []byte(`{"genesis_time":"0001-01-01T00:00:00Z","chain_id":"test-chain-QDKdJr","consensus_params":null,"validators":[{"pub_key":{"type":"ed25519","data":"961EAB8752E51A03618502F55C2B6E09C38C65635C64CCF3173ED452CF86C957"},"amount":10,"name":""}],"app_hash":""}`)
 	_, err := GenesisDocFromJSON(genDocBytes)
-	assert.Nil(t, err, "expected no error for good genDoc json")
+	assert.NoError(t, err, "expected no error for good genDoc json")
 
 	// create a base gendoc from struct
 	baseGenDoc := &GenesisDoc{
@@ -38,25 +39,25 @@ func TestGenesis(t *testing.T) {
 		Validators: []GenesisValidator{{crypto.GenPrivKeyEd25519().PubKey(), 10, "myval"}},
 	}
 	genDocBytes, err = json.Marshal(baseGenDoc)
-	assert.Nil(t, err, "error marshalling genDoc")
+	assert.NoError(t, err, "error marshalling genDoc")
 
 	// test base gendoc and check consensus params were filled
 	genDoc, err := GenesisDocFromJSON(genDocBytes)
-	assert.Nil(t, err, "expected no error for valid genDoc json")
+	assert.NoError(t, err, "expected no error for valid genDoc json")
 	assert.NotNil(t, genDoc.ConsensusParams, "expected consensus params to be filled in")
 
 	// create json with consensus params filled
 	genDocBytes, err = json.Marshal(genDoc)
-	assert.Nil(t, err, "error marshalling genDoc")
+	assert.NoError(t, err, "error marshalling genDoc")
 	genDoc, err = GenesisDocFromJSON(genDocBytes)
-	assert.Nil(t, err, "expected no error for valid genDoc json")
+	assert.NoError(t, err, "expected no error for valid genDoc json")
 
 	// test with invalid consensus params
 	genDoc.ConsensusParams.BlockSizeParams.MaxBytes = 0
 	genDocBytes, err = json.Marshal(genDoc)
-	assert.Nil(t, err, "error marshalling genDoc")
+	assert.NoError(t, err, "error marshalling genDoc")
 	genDoc, err = GenesisDocFromJSON(genDocBytes)
-	assert.NotNil(t, err, "expected error for genDoc json with block size of 0")
+	assert.Error(t, err, "expected error for genDoc json with block size of 0")
 }
 
 func newConsensusParams(blockSize, partSize int) *ConsensusParams {
@@ -80,9 +81,9 @@ func TestConsensusParams(t *testing.T) {
 	}
 	for _, testCase := range testCases {
 		if testCase.valid {
-			assert.Nil(t, testCase.params.Validate(), "expected no error for valid params")
+			assert.NoError(t, testCase.params.Validate(), "expected no error for valid params")
 		} else {
-			assert.NotNil(t, testCase.params.Validate(), "expected error for non valid params")
+			assert.Error(t, testCase.params.Validate(), "expected error for non valid params")
 		}
 	}
 }
diff --git a/types/params.go b/types/params.go
index 71ffe60c9..b55ceb8c3 100644
--- a/types/params.go
+++ b/types/params.go
@@ -4,6 +4,10 @@ import (
 	"github.com/pkg/errors"
 )
 
+const (
+	maxBlockSizeBytes = 104857600 // 100MB
+)
+
 // ConsensusParams contains consensus critical parameters
 // that determine the validity of blocks.
 type ConsensusParams struct {
@@ -66,11 +70,18 @@ func DefaultBlockGossipParams() *BlockGossipParams {
 // Validate validates the ConsensusParams to ensure all values
 // are within their allowed limits, and returns an error if they are not.
 func (params *ConsensusParams) Validate() error {
+	// ensure some values are greater than 0
 	if params.BlockSizeParams.MaxBytes <= 0 {
 		return errors.Errorf("BlockSizeParams.MaxBytes must be greater than 0. Got %d", params.BlockSizeParams.MaxBytes)
 	}
 	if params.BlockGossipParams.BlockPartSizeBytes <= 0 {
 		return errors.Errorf("BlockGossipParams.BlockPartSizeBytes must be greater than 0. Got %d", params.BlockGossipParams.BlockPartSizeBytes)
 	}
+
+	// ensure blocks aren't too big
+	if cp.BlockSizeParams.MaxBytes > maxBlockSizeBytes {
+		return errors.Errorf("BlockSizeParams.MaxBytes is too big. %d > %d",
+			cp.BlockSizeParams.MaxBytes, maxBlockSizeBytes)
+	}
 	return nil
 }