diff --git a/panda/src/gobj/geom.I b/panda/src/gobj/geom.I
index e54bd5dacb..edbd253e9b 100644
--- a/panda/src/gobj/geom.I
+++ b/panda/src/gobj/geom.I
@@ -138,6 +138,10 @@ get_texcoords_index() const {
 INLINE void Geom::
 set_num_prims(int num) {
   _numprims = num;
+  if (!uses_components()) {
+    // except for strips & fans with the length arrays, total verts will be simply this
+    _num_vertices = _numprims*get_num_vertices_per_prim();
+  }
   make_dirty();
 }
 
@@ -151,6 +155,30 @@ get_num_prims(void) const {
   return _numprims;
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: Geom::get_num_vertices
+//       Access: Public
+//  Description: Returns the number of vertices required by all all
+//               the prims in the Geom.
+////////////////////////////////////////////////////////////////////
+INLINE int Geom::
+get_num_vertices() const {
+  return _num_vertices;
+}
+
+INLINE int PTA_int_arraysum(const PTA_int &lengths) {
+    assert(lengths.size()>0);
+    
+    int *pLen=&lengths[0];
+    int *pArrayEnd=pLen+lengths.size();
+    int nVerts = 0;
+    for (;pLen<pArrayEnd;pLen++) {
+      nVerts += *pLen;
+    }
+    return nVerts;
+}
+
+
 ////////////////////////////////////////////////////////////////////
 //     Function: Geom::set_lengths
 //       Access: Public
@@ -163,6 +191,7 @@ get_num_prims(void) const {
 INLINE void Geom::
 set_lengths(const PTA_int &lengths) {
   _primlengths = lengths;
+  _num_vertices = PTA_int_arraysum(lengths);
   make_dirty();
 }
 
diff --git a/panda/src/gobj/geom.cxx b/panda/src/gobj/geom.cxx
index f67679811a..bc6045e507 100644
--- a/panda/src/gobj/geom.cxx
+++ b/panda/src/gobj/geom.cxx
@@ -187,6 +187,7 @@ operator = (const Geom &copy) {
   _tindex = copy._tindex;
 
   _numprims = copy._numprims;
+  _num_vertices = copy._num_vertices;
   _primlengths = copy._primlengths;
   for (int i = 0; i < num_GeomAttrTypes; i++) {
     _bind[i] = copy._bind[i];
@@ -355,26 +356,6 @@ is_dynamic() const {
   return (_vindex != (ushort*)0L);
 }
 
-////////////////////////////////////////////////////////////////////
-//     Function: Geom::get_num_vertices
-//       Access: Public
-//  Description: Returns the number of vertices required by all all
-//               the prims in the Geom.
-////////////////////////////////////////////////////////////////////
-int Geom::
-get_num_vertices() const {
-  if (!uses_components()) {
-    return get_num_vertices_per_prim() * get_num_prims();
-  }
-
-  int total = 0;
-  for (int i = 0; i < get_num_prims(); i++) {
-    total += _primlengths[i];
-  }
-
-  return total;
-}
-
 ////////////////////////////////////////////////////////////////////
 //     Function: Geom::explode
 //       Access: Public, Virtual
@@ -707,8 +688,17 @@ fillin(DatagramIterator& scan, BamReader* manager) {
   READ_PTA(manager, scan, IPD_ushort::read_datagram, _tindex)
 
   _numprims = scan.get_uint16();
+
+  // is there any point in doing this for uses_components()==false?
   READ_PTA(manager, scan, IPD_int::read_datagram, _primlengths)
 
+  if (uses_components()) {
+      _num_vertices = PTA_int_arraysum(_primlengths);
+  } else {
+      // except for strips & fans with the length arrays, total verts will be simply this
+      _num_vertices = _numprims*get_num_vertices_per_prim();
+  }
+
   //Write out the bindings for vertices, normals,
   //colors and texture coordinates
   for(i = 0; i < num_GeomAttrTypes; i++) {
diff --git a/panda/src/gobj/geom.h b/panda/src/gobj/geom.h
index 7aca16956f..02e6ac3a25 100644
--- a/panda/src/gobj/geom.h
+++ b/panda/src/gobj/geom.h
@@ -246,7 +246,7 @@ protected:
   PTA_ushort _cindex;
   PTA_ushort _tindex;
 
-  int _numprims;
+  int _numprims,_num_vertices;
   PTA_int _primlengths;
   enum GeomBindType _bind[num_GeomAttrTypes];