diff --git a/src/libbidir/edge.cpp b/src/libbidir/edge.cpp
index 6ad50fb1..4e867899 100644
--- a/src/libbidir/edge.cpp
+++ b/src/libbidir/edge.cpp
@@ -48,6 +48,9 @@ bool PathEdge::sampleNext(const Scene *scene, Sampler *sampler,
 		return false;
 	}
 
+	if (length == 0)
+		return false;
+
 	if (!medium) {
 		weight[ERadiance] = weight[EImportance] = Spectrum(1.0f);
 		pdf[ERadiance] = pdf[EImportance] = 1.0f;
@@ -103,6 +106,9 @@ bool PathEdge::perturbDirection(const Scene *scene,
 	}
 	d = ray.d;
 
+	if (length == 0)
+		return false;
+
 	if (!medium) {
 		weight[ERadiance] = weight[EImportance] = Spectrum(1.0f);
 		pdf[ERadiance] = pdf[EImportance] = 1.0f;