diff --git a/db/backend_test.go b/db/backend_test.go
index b4ffecdc..b21ce003 100644
--- a/db/backend_test.go
+++ b/db/backend_test.go
@@ -2,42 +2,79 @@ package db
 
 import (
 	"fmt"
+	"os"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	cmn "github.com/tendermint/tmlibs/common"
 )
 
-func testBackend(t *testing.T, backend string) {
+func testBackendGetSetDelete(t *testing.T, backend string) {
 	// Default
 	dir, dirname := cmn.Tempdir(fmt.Sprintf("test_backend_%s_", backend))
 	defer dir.Close()
 	db := NewDB("testdb", backend, dirname)
 	require.Nil(t, db.Get([]byte("")))
-	require.Nil(t, db.Get(nil))
 
 	// Set empty ("")
 	db.Set([]byte(""), []byte(""))
 	require.NotNil(t, db.Get([]byte("")))
-	require.NotNil(t, db.Get(nil))
 	require.Empty(t, db.Get([]byte("")))
-	require.Empty(t, db.Get(nil))
 
 	// Set empty (nil)
 	db.Set([]byte(""), nil)
 	require.NotNil(t, db.Get([]byte("")))
-	require.NotNil(t, db.Get(nil))
 	require.Empty(t, db.Get([]byte("")))
-	require.Empty(t, db.Get(nil))
 
 	// Delete
 	db.Delete([]byte(""))
 	require.Nil(t, db.Get([]byte("")))
-	require.Nil(t, db.Get(nil))
 }
 
-func TestBackends(t *testing.T) {
-	testBackend(t, CLevelDBBackendStr)
-	testBackend(t, GoLevelDBBackendStr)
-	testBackend(t, MemDBBackendStr)
+func TestBackendsGetSetDelete(t *testing.T) {
+	for dbType, _ := range backends {
+		if dbType == "fsdb" {
+			// TODO: handle
+			// fsdb cant deal with length 0 keys
+			continue
+		}
+		testBackendGetSetDelete(t, dbType)
+	}
+}
+
+func assertPanics(t *testing.T, dbType, name string, fn func()) {
+	defer func() {
+		r := recover()
+		assert.NotNil(t, r, cmn.Fmt("expecting %s.%s to panic", dbType, name))
+	}()
+
+	fn()
+}
+
+func TestBackendsNilKeys(t *testing.T) {
+	// test all backends
+	for dbType, creator := range backends {
+		name := cmn.Fmt("test_%x", cmn.RandStr(12))
+		db, err := creator(name, "")
+		assert.Nil(t, err)
+		defer os.RemoveAll(name)
+
+		assertPanics(t, dbType, "get", func() { db.Get(nil) })
+		assertPanics(t, dbType, "has", func() { db.Has(nil) })
+		assertPanics(t, dbType, "set", func() { db.Set(nil, []byte("abc")) })
+		assertPanics(t, dbType, "setsync", func() { db.SetSync(nil, []byte("abc")) })
+		assertPanics(t, dbType, "delete", func() { db.Delete(nil) })
+		assertPanics(t, dbType, "deletesync", func() { db.DeleteSync(nil) })
+
+		db.Close()
+	}
+}
+
+func TestLevelDBBackendStr(t *testing.T) {
+	name := cmn.Fmt("test_%x", cmn.RandStr(12))
+	db := NewDB(name, LevelDBBackendStr, "")
+	defer os.RemoveAll(name)
+	_, ok := db.(*GoLevelDB)
+	assert.True(t, ok)
 }
diff --git a/db/fsdb.go b/db/fsdb.go
index b6e08daf..19ea9fa3 100644
--- a/db/fsdb.go
+++ b/db/fsdb.go
@@ -44,6 +44,7 @@ func NewFSDB(dir string) *FSDB {
 func (db *FSDB) Get(key []byte) []byte {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
+	panicNilKey(key)
 
 	path := db.nameToPath(key)
 	value, err := read(path)
@@ -58,6 +59,7 @@ func (db *FSDB) Get(key []byte) []byte {
 func (db *FSDB) Has(key []byte) bool {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
+	panicNilKey(key)
 
 	path := db.nameToPath(key)
 	_, err := read(path)
@@ -72,6 +74,7 @@ func (db *FSDB) Has(key []byte) bool {
 func (db *FSDB) Set(key []byte, value []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
+	panicNilKey(key)
 
 	db.SetNoLock(key, value)
 }
@@ -79,12 +82,14 @@ func (db *FSDB) Set(key []byte, value []byte) {
 func (db *FSDB) SetSync(key []byte, value []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
+	panicNilKey(key)
 
 	db.SetNoLock(key, value)
 }
 
 // NOTE: Implements atomicSetDeleter.
 func (db *FSDB) SetNoLock(key []byte, value []byte) {
+	panicNilKey(key)
 	if value == nil {
 		value = []byte{}
 	}
@@ -98,6 +103,7 @@ func (db *FSDB) SetNoLock(key []byte, value []byte) {
 func (db *FSDB) Delete(key []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
+	panicNilKey(key)
 
 	db.DeleteNoLock(key)
 }
@@ -105,12 +111,14 @@ func (db *FSDB) Delete(key []byte) {
 func (db *FSDB) DeleteSync(key []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
+	panicNilKey(key)
 
 	db.DeleteNoLock(key)
 }
 
 // NOTE: Implements atomicSetDeleter.
 func (db *FSDB) DeleteNoLock(key []byte) {
+	panicNilKey(key)
 	err := remove(string(key))
 	if os.IsNotExist(err) {
 		return
diff --git a/db/go_level_db.go b/db/go_level_db.go
index e8ed99de..201a3194 100644
--- a/db/go_level_db.go
+++ b/db/go_level_db.go
@@ -37,6 +37,7 @@ func NewGoLevelDB(name string, dir string) (*GoLevelDB, error) {
 }
 
 func (db *GoLevelDB) Get(key []byte) []byte {
+	panicNilKey(key)
 	res, err := db.db.Get(key, nil)
 	if err != nil {
 		if err == errors.ErrNotFound {
@@ -49,6 +50,7 @@ func (db *GoLevelDB) Get(key []byte) []byte {
 }
 
 func (db *GoLevelDB) Has(key []byte) bool {
+	panicNilKey(key)
 	_, err := db.db.Get(key, nil)
 	if err != nil {
 		if err == errors.ErrNotFound {
@@ -61,6 +63,7 @@ func (db *GoLevelDB) Has(key []byte) bool {
 }
 
 func (db *GoLevelDB) Set(key []byte, value []byte) {
+	panicNilKey(key)
 	err := db.db.Put(key, value, nil)
 	if err != nil {
 		PanicCrisis(err)
@@ -68,6 +71,7 @@ func (db *GoLevelDB) Set(key []byte, value []byte) {
 }
 
 func (db *GoLevelDB) SetSync(key []byte, value []byte) {
+	panicNilKey(key)
 	err := db.db.Put(key, value, &opt.WriteOptions{Sync: true})
 	if err != nil {
 		PanicCrisis(err)
@@ -75,6 +79,7 @@ func (db *GoLevelDB) SetSync(key []byte, value []byte) {
 }
 
 func (db *GoLevelDB) Delete(key []byte) {
+	panicNilKey(key)
 	err := db.db.Delete(key, nil)
 	if err != nil {
 		PanicCrisis(err)
@@ -82,6 +87,7 @@ func (db *GoLevelDB) Delete(key []byte) {
 }
 
 func (db *GoLevelDB) DeleteSync(key []byte) {
+	panicNilKey(key)
 	err := db.db.Delete(key, &opt.WriteOptions{Sync: true})
 	if err != nil {
 		PanicCrisis(err)
diff --git a/db/mem_db.go b/db/mem_db.go
index 3127030a..ebeb2dde 100644
--- a/db/mem_db.go
+++ b/db/mem_db.go
@@ -27,14 +27,14 @@ func NewMemDB() *MemDB {
 func (db *MemDB) Get(key []byte) []byte {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
-
+	panicNilKey(key)
 	return db.db[string(key)]
 }
 
 func (db *MemDB) Has(key []byte) bool {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
-
+	panicNilKey(key)
 	_, ok := db.db[string(key)]
 	return ok
 }
@@ -42,14 +42,14 @@ func (db *MemDB) Has(key []byte) bool {
 func (db *MemDB) Set(key []byte, value []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
-
+	panicNilKey(key)
 	db.SetNoLock(key, value)
 }
 
 func (db *MemDB) SetSync(key []byte, value []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
-
+	panicNilKey(key)
 	db.SetNoLock(key, value)
 }
 
@@ -58,25 +58,27 @@ func (db *MemDB) SetNoLock(key []byte, value []byte) {
 	if value == nil {
 		value = []byte{}
 	}
+	panicNilKey(key)
 	db.db[string(key)] = value
 }
 
 func (db *MemDB) Delete(key []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
-
+	panicNilKey(key)
 	delete(db.db, string(key))
 }
 
 func (db *MemDB) DeleteSync(key []byte) {
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
-
+	panicNilKey(key)
 	delete(db.db, string(key))
 }
 
 // NOTE: Implements atomicSetDeleter
 func (db *MemDB) DeleteNoLock(key []byte) {
+	panicNilKey(key)
 	delete(db.db, string(key))
 }
 
diff --git a/db/types.go b/db/types.go
index a6edbdd8..54c1025a 100644
--- a/db/types.go
+++ b/db/types.go
@@ -121,3 +121,10 @@ type Iterator interface {
 func bz(s string) []byte {
 	return []byte(s)
 }
+
+// All DB funcs should panic on nil key.
+func panicNilKey(key []byte) {
+	if key == nil {
+		panic("nil key")
+	}
+}