diff --git a/input_definition.go b/input_definition.go
index c83a43f5b..6a580a48b 100644
--- a/input_definition.go
+++ b/input_definition.go
@@ -253,6 +253,15 @@ func convert(x *uint64) uint64 {
 	return 0
 }
 
+func convert(x *uint64) uint64 {
+	if x != nil {
+		return *x
+	}
+	var v int64 = -1
+	var v2 uint64 = uint64(v)
+	return v2
+}
+
 // InputFrame defines the frame used in the input definition.
 type InputFrame struct {
 	Name    string       `json:"name,omitempty"`