diff --git a/src/mesh/marching_cubes.cpp b/src/mesh/marching_cubes.cpp
index 8bdc282..815761f 100644
--- a/src/mesh/marching_cubes.cpp
+++ b/src/mesh/marching_cubes.cpp
@@ -131,7 +131,8 @@ MCMesh marching_cubes(const std::function<double(double,double,double)>& f,
                 if (edge_mask == 0) continue;
 
                 // Compute interpolated vertices for intersected edges
-                int vert_idx[12] = {-1};
+                int vert_idx[12];
+                for (int& v : vert_idx) v = -1;
                 for (int e = 0; e < 12; ++e) {
                     if (!(edge_mask & (1 << e))) continue;
                     int v0 = kEdgeCorners[e][0], v1 = kEdgeCorners[e][1];
@@ -148,10 +149,12 @@ MCMesh marching_cubes(const std::function<double(double,double,double)>& f,
                     }
                 }
 
-                // Triangulate from standard table
+                // Triangulate from standard table (validate entries: 0..11)
                 const int* tris = kTriTable[cube_idx];
-                for (int t = 0; tris[t] != -1; t += 3) {
-                    if (tris[t+2] == -1) break;
+                for (int t = 0; t < 15 && tris[t] != -1; t += 3) {
+                    if (tris[t] < 0 || tris[t] > 11 || tris[t+1] < 0 || tris[t+1] > 11
+                        || tris[t+2] < 0 || tris[t+2] > 11) break;
+                    if (vert_idx[tris[t]] < 0 || vert_idx[tris[t+1]] < 0 || vert_idx[tris[t+2]] < 0) break;
                     result.triangles.push_back({
                         vert_idx[tris[t]], vert_idx[tris[t+1]], vert_idx[tris[t+2]]
                     });