diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..aaea8ed
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+cid-fuzz.zip
diff --git a/cid_fuzz.go b/cid_fuzz.go
index 495ec4d..0d47167 100644
--- a/cid_fuzz.go
+++ b/cid_fuzz.go
@@ -10,8 +10,26 @@ func Fuzz(data []byte) int {
 	}
 
 	_ = cid.Bytes()
+	_ = cid.String()
+	_ = cid.Prefix()
+
 	if !cid.Equals(cid) {
 		panic("inequality")
 	}
+
+	// json loop
+	json, err := cid.MarshalJSON()
+	if err != nil {
+		panic(err.Error())
+	}
+	cid2 := &Cid{}
+	err = cid2.UnmarshalJSON(json)
+	if err != nil {
+		panic(err.Error())
+	}
+
+	if !cid.Equals(cid2) {
+		panic("json loop not equal")
+	}
 	return 1
 }