diff --git a/generic.go b/generic.go
index 7c977b9..8d6f441 100644
--- a/generic.go
+++ b/generic.go
@@ -3,12 +3,20 @@ package monstersirenfetch
 import (
 	"encoding/json"
 	"strconv"
+	"strings"
 )
 
 // StringInt is a JSON string representing an integer.
 type StringInt int
 
-func (i *StringInt) MarshalJSON() ([]byte, error) { return json.Marshal(strconv.Itoa(int(*i))) }
+func (i *StringInt) MarshalJSON() ([]byte, error) {
+	s := strconv.Itoa(int(*i))
+	if len(s) < 4 {
+		s = strings.Repeat("0", 4-len(s)) + s
+	}
+	return json.Marshal(s)
+}
+
 func (i *StringInt) UnmarshalJSON(data []byte) (err error) {
 	var v string
 	err = json.Unmarshal(data, &v)
diff --git a/generic_test.go b/generic_test.go
index 84d4485..1d7f04c 100644
--- a/generic_test.go
+++ b/generic_test.go
@@ -18,6 +18,7 @@ func TestStringInt(t *testing.T) {
 		val     int
 	}{
 		{"valid", nil, `"3735928559"`, 0xdeadbeef},
+		{"valid pad", nil, `"0009"`, 9},
 		{"invalid json", newSyntaxError("unexpected end of JSON input", 11), `"3735928559`, -1},
 		{"invalid number", &strconv.NumError{Func: "Atoi", Num: ":3735928559", Err: strconv.ErrSyntax}, `":3735928559"`, -1},
 	}