diff --git a/d2plugin/exec.go b/d2plugin/exec.go
index b004b5aff..acb8a9618 100644
--- a/d2plugin/exec.go
+++ b/d2plugin/exec.go
@@ -126,7 +126,7 @@ func (p execPlugin) Layout(ctx context.Context, g *d2graph.Graph) error {
 
 	args := []string{"layout"}
 	for k, v := range p.opts {
-		args = append(args, k, v)
+		args = append(args, fmt.Sprintf("--%s", k), v)
 	}
 	cmd := exec.CommandContext(ctx, p.path, args...)
 
diff --git a/d2plugin/plugin.go b/d2plugin/plugin.go
index 765d9f60e..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)
 	}
 }
 
@@ -142,5 +150,19 @@ func ListPluginFlags(ctx context.Context) ([]PluginSpecificFlag, error) {
 		}
 		out = append(out, flags...)
 	}
+
+	matches, err := xexec.SearchPath(binaryPrefix)
+	if err != nil {
+		return nil, err
+	}
+	for _, path := range matches {
+		p := &execPlugin{path: path}
+		flags, err := p.Flags(ctx)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, flags...)
+	}
+
 	return out, nil
 }
diff --git a/d2plugin/serve.go b/d2plugin/serve.go
index cf857b3ee..2e8da78f0 100644
--- a/d2plugin/serve.go
+++ b/d2plugin/serve.go
@@ -21,6 +21,13 @@ import (
 // Also see execPlugin in exec.go for the d2 binary plugin protocol.
 func Serve(p Plugin) xmain.RunFunc {
 	return func(ctx context.Context, ms *xmain.State) (err error) {
+		fs, err := p.Flags(ctx)
+		if err != nil {
+			return err
+		}
+		for _, f := range fs {
+			f.AddToOpts(ms.Opts)
+		}
 		err = ms.Opts.Flags.Parse(ms.Opts.Args)
 		if !errors.Is(err, pflag.ErrHelp) && err != nil {
 			return xmain.UsageErrorf("failed to parse flags: %v", err)