diff --git a/src/testrender/bvh.cpp b/src/testrender/bvh.cpp
index 92eb0e5bb..2a81c27da 100644
--- a/src/testrender/bvh.cpp
+++ b/src/testrender/bvh.cpp
@@ -148,6 +148,9 @@ build_bvh(OIIO::cspan<Vec3> verts, OIIO::cspan<TriangleIndices> triangles,
                     float center  = bbox.center()[bestAxis];
                     int binID = (int)((center - current.centroid.min[bestAxis])
                                       * binFactor[bestAxis]);
+                    if (!(binID >= 0 && binID < NumBins)) {
+                        print("binID {} NumBins {}  i={}\n", binID, NumBins, i);
+                    }
                     OSL_ASSERT(binID >= 0 && binID < NumBins);
                     if (binID <= bestBin) {
                         boundsL.extendBy(bbox);