diff --git a/gtk2_ardour/export_analysis_graphs.cc b/gtk2_ardour/export_analysis_graphs.cc
index 97190260f4..45d231e575 100644
--- a/gtk2_ardour/export_analysis_graphs.cc
+++ b/gtk2_ardour/export_analysis_graphs.cc
@@ -243,9 +243,11 @@ ArdourGraphs::draw_spectrum (Glib::RefPtr<Pango::Context> pctx, ExportAnalysisPt
 	int w, h, anw;
 	const size_t width = p->width;
 
-	assert (height == p->spectrum[0].size ());
+	typedef std::vector<double> Dashes;
+	Dashes dashes;
+
+	assert ((Dashes::size_type) height == p->spectrum[0].size ());
 
-	std::vector<double> dashes;
 	dashes.push_back (3.0);
 	dashes.push_back (5.0);