diff --git a/CHANGELOG_PENDING.md b/CHANGELOG_PENDING.md
index c0e25dec8..34af3432c 100644
--- a/CHANGELOG_PENDING.md
+++ b/CHANGELOG_PENDING.md
@@ -15,7 +15,7 @@ BREAKING CHANGES:
   * [genesis] \#2565 `consensus_params.evidence_params.max_age` is now `time.Duration` (nanosecond count)
         ```json
         "evidence_params": {
-          "max_age": "172800000000000"
+          "max_age": "48h0m0s"
         }
         ```
 
diff --git a/evidence/pool.go b/evidence/pool.go
index 3ad715632..97fbd37d7 100644
--- a/evidence/pool.go
+++ b/evidence/pool.go
@@ -129,7 +129,7 @@ func (evpool *EvidencePool) MarkEvidenceAsCommitted(evidence []types.Evidence, l
 	}
 
 	// remove committed evidence from the clist
-	maxAge := evpool.State().ConsensusParams.EvidenceParams.MaxAge
+	maxAge := evpool.State().ConsensusParams.EvidenceParams.MaxAge.Duration
 	evpool.removeEvidence(blockEvidenceMap, lastBlockTime, maxAge)
 }
 
diff --git a/evidence/pool_test.go b/evidence/pool_test.go
index c3ed569e1..4adb1f8ba 100644
--- a/evidence/pool_test.go
+++ b/evidence/pool_test.go
@@ -39,7 +39,7 @@ func initializeValidatorState(valAddr []byte, height int64) dbm.DB {
 		LastHeightValidatorsChanged: 1,
 		ConsensusParams: types.ConsensusParams{
 			EvidenceParams: types.EvidenceParams{
-				MaxAge: 1000000,
+				MaxAge: tmtime.DurationPretty{1000000},
 			},
 		},
 	}
diff --git a/state/state_test.go b/state/state_test.go
index 3ffbb8f2b..b6bc9e767 100644
--- a/state/state_test.go
+++ b/state/state_test.go
@@ -13,6 +13,7 @@ import (
 	"github.com/tendermint/tendermint/crypto/ed25519"
 	cmn "github.com/tendermint/tendermint/libs/common"
 	dbm "github.com/tendermint/tendermint/libs/db"
+	tmtime "github.com/tendermint/tendermint/types/time"
 
 	cfg "github.com/tendermint/tendermint/config"
 	"github.com/tendermint/tendermint/types"
@@ -394,7 +395,7 @@ func makeParams(blockBytes, blockGas int64, evidenceAge time.Duration) types.Con
 			MaxGas:   blockGas,
 		},
 		EvidenceParams: types.EvidenceParams{
-			MaxAge: evidenceAge,
+			MaxAge: tmtime.DurationPretty{evidenceAge},
 		},
 	}
 }
diff --git a/state/validation.go b/state/validation.go
index 14e4ff9da..38aff6820 100644
--- a/state/validation.go
+++ b/state/validation.go
@@ -169,7 +169,7 @@ func validateBlock(stateDB dbm.DB, state State, block *types.Block) error {
 // - it was properly signed by the alleged equivocator
 func VerifyEvidence(stateDB dbm.DB, state State, evidence types.Evidence) error {
 	evidenceAge := state.LastBlockTime.Sub(evidence.Time())
-	maxAge := state.ConsensusParams.EvidenceParams.MaxAge
+	maxAge := state.ConsensusParams.EvidenceParams.MaxAge.Duration
 	if evidenceAge > maxAge {
 		return fmt.Errorf("Evidence from %v is too old. Expecting evidence no older than %v",
 			evidence.Time(), state.LastBlockTime.Add(-maxAge))
diff --git a/types/params.go b/types/params.go
index 85b4cf0e3..858cbd930 100644
--- a/types/params.go
+++ b/types/params.go
@@ -6,6 +6,7 @@ import (
 	abci "github.com/tendermint/tendermint/abci/types"
 	"github.com/tendermint/tendermint/crypto/tmhash"
 	cmn "github.com/tendermint/tendermint/libs/common"
+	tmtime "github.com/tendermint/tendermint/types/time"
 )
 
 const (
@@ -31,7 +32,7 @@ type BlockSize struct {
 
 // EvidenceParams determine how we handle evidence of malfeasance
 type EvidenceParams struct {
-	MaxAge time.Duration `json:"max_age"` // only accept new evidence more recent than this
+	MaxAge tmtime.DurationPretty `json:"max_age"` // only accept new evidence more recent than this
 }
 
 // DefaultConsensusParams returns a default ConsensusParams.
@@ -53,7 +54,7 @@ func DefaultBlockSize() BlockSize {
 // DefaultEvidenceParams Params returns a default EvidenceParams.
 func DefaultEvidenceParams() EvidenceParams {
 	return EvidenceParams{
-		MaxAge: 48 * time.Hour,
+		MaxAge: tmtime.DurationPretty{48 * time.Hour},
 	}
 }
 
@@ -74,9 +75,9 @@ func (params *ConsensusParams) Validate() error {
 			params.BlockSize.MaxGas)
 	}
 
-	if params.EvidenceParams.MaxAge <= 0 {
+	if params.EvidenceParams.MaxAge.Duration <= 0 {
 		return cmn.NewError("EvidenceParams.MaxAge must be greater than 0. Got %d",
-			params.EvidenceParams.MaxAge)
+			params.EvidenceParams.MaxAge.Duration)
 	}
 
 	return nil
@@ -111,7 +112,7 @@ func (params ConsensusParams) Update(params2 *abci.ConsensusParams) ConsensusPar
 		res.BlockSize.MaxGas = params2.BlockSize.MaxGas
 	}
 	if params2.EvidenceParams != nil {
-		res.EvidenceParams.MaxAge = params2.EvidenceParams.MaxAge
+		res.EvidenceParams.MaxAge = tmtime.DurationPretty{params2.EvidenceParams.MaxAge}
 	}
 	return res
 }
diff --git a/types/params_test.go b/types/params_test.go
index 5491c3464..c16c44b8f 100644
--- a/types/params_test.go
+++ b/types/params_test.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	abci "github.com/tendermint/tendermint/abci/types"
+	tmtime "github.com/tendermint/tendermint/types/time"
 )
 
 func TestConsensusParamsValidation(t *testing.T) {
@@ -44,7 +45,7 @@ func makeParams(blockBytes, blockGas int64, evidenceAge time.Duration) Consensus
 			MaxGas:   blockGas,
 		},
 		EvidenceParams: EvidenceParams{
-			MaxAge: evidenceAge,
+			MaxAge: tmtime.DurationPretty{evidenceAge},
 		},
 	}
 }
diff --git a/types/protobuf.go b/types/protobuf.go
index 332a23dc0..6d5add70a 100644
--- a/types/protobuf.go
+++ b/types/protobuf.go
@@ -9,6 +9,7 @@ import (
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/crypto/ed25519"
 	"github.com/tendermint/tendermint/crypto/secp256k1"
+	tmtime "github.com/tendermint/tendermint/types/time"
 )
 
 //-------------------------------------------------------
@@ -119,7 +120,7 @@ func (tm2pb) ConsensusParams(params *ConsensusParams) *abci.ConsensusParams {
 			MaxGas:   params.BlockSize.MaxGas,
 		},
 		EvidenceParams: &abci.EvidenceParams{
-			MaxAge: params.EvidenceParams.MaxAge,
+			MaxAge: params.EvidenceParams.MaxAge.Duration,
 		},
 	}
 }
@@ -219,7 +220,7 @@ func (pb2tm) ConsensusParams(csp *abci.ConsensusParams) ConsensusParams {
 		}
 	}
 	if csp.EvidenceParams != nil {
-		params.EvidenceParams.MaxAge = csp.EvidenceParams.MaxAge
+		params.EvidenceParams.MaxAge = tmtime.DurationPretty{csp.EvidenceParams.MaxAge}
 	}
 
 	return params
diff --git a/types/protobuf_test.go b/types/protobuf_test.go
index f8682abf8..32b5417f7 100644
--- a/types/protobuf_test.go
+++ b/types/protobuf_test.go
@@ -68,7 +68,7 @@ func TestABCIValidators(t *testing.T) {
 
 func TestABCIConsensusParams(t *testing.T) {
 	cp := DefaultConsensusParams()
-	cp.EvidenceParams.MaxAge = 0 // TODO add this to ABCI
+	cp.EvidenceParams.MaxAge.Duration = 0 // TODO add this to ABCI
 	abciCP := TM2PB.ConsensusParams(cp)
 	cp2 := PB2TM.ConsensusParams(abciCP)
 
diff --git a/types/time/duration.go b/types/time/duration.go
new file mode 100644
index 000000000..3df174302
--- /dev/null
+++ b/types/time/duration.go
@@ -0,0 +1,41 @@
+package time
+
+import (
+	"encoding/json"
+	"errors"
+	"time"
+)
+
+// DurationPretty is a wrapper around time.Duration implementing custom
+// marshaller/unmarshaller which make it pretty (e.g. "10s", not
+// "10000000000").
+type DurationPretty struct {
+	time.Duration
+}
+
+// MarshalJSON implements json.Marshaller.
+func (d DurationPretty) MarshalJSON() ([]byte, error) {
+	return json.Marshal(d.String())
+}
+
+// UnmarshalJSON implements json.Unmarshaller.
+func (d *DurationPretty) UnmarshalJSON(b []byte) error {
+	var v interface{}
+	if err := json.Unmarshal(b, &v); err != nil {
+		return err
+	}
+	switch value := v.(type) {
+	case float64:
+		d.Duration = time.Duration(value)
+		return nil
+	case string:
+		var err error
+		d.Duration, err = time.ParseDuration(value)
+		if err != nil {
+			return err
+		}
+		return nil
+	default:
+		return errors.New("invalid duration")
+	}
+}