diff --git a/zpay32/fuzz_test.go b/zpay32/fuzz_test.go
index 5b7897998..696b09c3a 100644
--- a/zpay32/fuzz_test.go
+++ b/zpay32/fuzz_test.go
@@ -1,6 +1,7 @@
 package zpay32
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/btcsuite/btcd/chaincfg"
@@ -12,9 +13,44 @@ func FuzzDecode(f *testing.F) {
 	})
 }
 
+// appendChecksum returns a string containing bech followed by its bech32
+// checksum if a checksum could be calculated. Otherwise, the function returns
+// bech unchanged.
+//
+// This code is based on checksum calculation in zpay32/bech32.go.
+func appendChecksum(bech string) string {
+	lower := strings.ToLower(bech)
+
+	// The string is invalid if the last '1' is non-existent or it is the
+	// first character of the string (no human-readable part).
+	one := strings.LastIndexByte(lower, '1')
+	if one < 1 {
+		return bech
+	}
+	hrp := lower[:one]
+	data := lower[one+1:]
+
+	decoded, err := toBytes(data)
+	if err != nil {
+		return bech
+	}
+
+	checksum, err := toChars(bech32Checksum(hrp, decoded))
+	if err != nil {
+		return bech
+	}
+
+	return bech + checksum
+}
+
 func FuzzEncode(f *testing.F) {
 	f.Fuzz(func(t *testing.T, data string) {
-		inv, err := Decode(data, &chaincfg.TestNet3Params)
+		// Make it easier for the fuzzer to generate valid invoice
+		// encodings by adding the required prefix and valid checksum.
+		data = "lnbc" + data
+		data = appendChecksum(data)
+
+		inv, err := Decode(data, &chaincfg.MainNetParams)
 		if err != nil {
 			return
 		}