diff --git a/concrete/densegraph_test.go b/concrete/densegraph_test.go
new file mode 100644
index 00000000..f48888ba
--- /dev/null
+++ b/concrete/densegraph_test.go
@@ -0,0 +1,9 @@
+package concrete_test
+
+import (
+	"github.com/gonum/graph"
+	"github.com/gonum/graph/concrete"
+)
+
+var _ graph.DirectedGraph = &concrete.DenseGraph{}
+var _ graph.CrunchGraph = &concrete.DenseGraph{}