diff --git a/d2plugin/plugin.go b/d2plugin/plugin.go
index 38eade4a9..a8c894333 100644
--- a/d2plugin/plugin.go
+++ b/d2plugin/plugin.go
@@ -34,7 +34,15 @@ func (f *PluginSpecificFlag) AddToOpts(opts *xmain.Opts) {
 	case "string":
 		opts.String("", f.Name, "", f.Default.(string), f.Usage)
 	case "int64":
-		opts.Int64("", f.Name, "", f.Default.(int64), f.Usage)
+		var val int64
+		switch defaultType := f.Default.(type) {
+		case int64:
+			val = defaultType
+		case float64:
+			// json unmarshals numbers to float64
+			val = int64(defaultType)
+		}
+		opts.Int64("", f.Name, "", val, f.Usage)
 	}
 }