diff --git a/core/rawdb/accessors_chain.go b/core/rawdb/accessors_chain.go
index e61559993c..5a4af5bb87 100644
--- a/core/rawdb/accessors_chain.go
+++ b/core/rawdb/accessors_chain.go
@@ -316,8 +316,8 @@ func ReadHeaderRange(db ethdb.Reader, number uint64, count uint64) []rlp.RawValu
 	if count == 0 {
 		return rlpHeaders
 	}
-	// read remaining from ancients
-	data, err := db.AncientRange(ChainFreezerHeaderTable, i+1-count, count, 0)
+	// read remaining from ancients, cap at 2M
+	data, err := db.AncientRange(ChainFreezerHeaderTable, i+1-count, count, 2*1024*1024)
 	if err != nil {
 		log.Error("Failed to read headers from freezer", "err", err)
 		return rlpHeaders
diff --git a/eth/filters/api.go b/eth/filters/api.go
index 59103ac03c..56a9de1b21 100644
--- a/eth/filters/api.go
+++ b/eth/filters/api.go
@@ -43,6 +43,9 @@ var (
 // The maximum number of topic criteria allowed, vm.LOG4 - vm.LOG0
 const maxTopics = 4
 
+// The maximum number of allowed topics within a topic criteria
+const maxSubTopics = 1000
+
 // filter is a helper struct that holds meta information over the filter type
 // and associated subscription in the event system.
 type filter struct {
@@ -539,6 +542,9 @@ func (args *FilterCriteria) UnmarshalJSON(data []byte) error {
 			return errors.New("invalid addresses in query")
 		}
 	}
+	if len(raw.Topics) > maxTopics {
+		return errExceedMaxTopics
+	}
 
 	// topics is an array consisting of strings and/or arrays of strings.
 	// JSON null values are converted to common.Hash{} and ignored by the filter manager.
@@ -559,6 +565,9 @@ func (args *FilterCriteria) UnmarshalJSON(data []byte) error {
 
 			case []interface{}:
 				// or case e.g. [null, "topic0", "topic1"]
+				if len(topic) > maxSubTopics {
+					return errExceedMaxTopics
+				}
 				for _, rawTopic := range topic {
 					if rawTopic == nil {
 						// null component, match all
diff --git a/p2p/nat/natpmp.go b/p2p/nat/natpmp.go
index ea2d897829..94ef1f4b68 100644
--- a/p2p/nat/natpmp.go
+++ b/p2p/nat/natpmp.go
@@ -26,7 +26,7 @@ import (
 	natpmp "github.com/jackpal/go-nat-pmp"
 )
 
-// natPMPClient adapts the NAT-PMP protocol implementation so it conforms to
+// pmp adapts the NAT-PMP protocol implementation so it conforms to
 // the common interface.
 type pmp struct {
 	gw net.IP
diff --git a/p2p/nat/natupnp.go b/p2p/nat/natupnp.go
index c90c4f3de8..f1bb955892 100644
--- a/p2p/nat/natupnp.go
+++ b/p2p/nat/natupnp.go
@@ -205,8 +205,8 @@ func discoverUPnP() Interface {
 	return nil
 }
 
-// finds devices matching the given target and calls matcher for all
-// advertised services of each device. The first non-nil service found
+// discover finds devices matching the given target and calls matcher for
+// all advertised services of each device. The first non-nil service found
 // is sent into out. If no service matched, nil is sent.
 func discover(out chan<- *upnp, target string, matcher func(goupnp.ServiceClient) *upnp) {
 	devs, err := goupnp.DiscoverDevices(target)