diff --git a/libs/ardour/vst_plugin.cc b/libs/ardour/vst_plugin.cc
index dbc64f1ea8..3a77fc4d9f 100644
--- a/libs/ardour/vst_plugin.cc
+++ b/libs/ardour/vst_plugin.cc
@@ -103,7 +103,7 @@ VSTPlugin::set_parameter (uint32_t which, float val)
 {
 	float v = get_parameter (which);
 
-	cerr << name() << " setting parameter #" << which << " to " << val << " current " << v << " == ? " << (v == val) << endl;
+	cerr << name() << " setting parameter #" << which << " to " << val << " current " << v << " == ? " << (v == val) << " delta " << std::setprecision(15) << (v - val) << endl;
 
 	if (get_parameter (which) == val) {
 		return;