diff --git a/libraries/fbx/src/GLTFSerializer.cpp b/libraries/fbx/src/GLTFSerializer.cpp
index cd2e4e2720..337c9d7f70 100755
--- a/libraries/fbx/src/GLTFSerializer.cpp
+++ b/libraries/fbx/src/GLTFSerializer.cpp
@@ -1593,11 +1593,15 @@ bool GLTFSerializer::buildGeometry(HFMModel& hfmModel, const hifi::VariantHash&
                             generateTargetData(target.values.value((QString) "POSITION"), weight, vertices);
                         }
 
-                        auto blendshapeIndicesCount = blendshape.indices.count();
+                        if (blendshape.indices.size() < prevMeshVerticesCount + vertices.size()) {
+                            blendshape.indices.resize(prevMeshVerticesCount + vertices.size());
+                            blendshape.vertices.resize(prevMeshVerticesCount + vertices.size());
+                            blendshape.normals.resize(prevMeshVerticesCount + vertices.size());
+                        }
                         for (int i = 0; i < vertices.size(); i++) {
-                            blendshape.indices.push_back(blendshapeIndicesCount + i);
-                            blendshape.vertices.push_back(vertices.value(i));
-                            blendshape.normals.push_back(normals.value(i));
+                            blendshape.indices[prevMeshVerticesCount + i] = prevMeshVerticesCount + i;
+                            blendshape.vertices[prevMeshVerticesCount + i] += vertices.value(i);
+                            blendshape.normals[prevMeshVerticesCount + i] += normals.value(i);
                         }
 
                     }