diff --git a/GPy/core/parameterization/ties_and_remappings.py b/GPy/core/parameterization/ties_and_remappings.py
index d3456c79..4da59237 100644
--- a/GPy/core/parameterization/ties_and_remappings.py
+++ b/GPy/core/parameterization/ties_and_remappings.py
@@ -477,30 +477,31 @@ class Tie(Parameterized):
             self.buf_idx = self._highest_parent_._raveled_index_for(self.tied_param)
             self._untie_ = self.label_buf==0
             self._untie_[self.buf_idx] = True
-            self.tie_pairs = np.empty(((self.label_buf>0).sum()-self.tied_param.size,2),dtype=np.uint32)
-            try:
-                from scipy import weave
-                self._label_to_idx = np.zeros((self.tied_param.tie.max()+1,),dtype=np.int32)
-                self._label_to_idx[self.tied_param.tie] = range(self.tied_param.size)
-                ltoi = self._label_to_idx
-                t_start=int(self.buf_idx[0])
-                t_end=int(self.buf_idx[-1])
-                label_buf = self.label_buf
-                buf_size = self.label_buf.size
-                t_pairs = self.tie_pairs
-                code = """
-                int j=0;
-                for(int i=0;i<buf_size;i++) {
-                    if(label_buf[i]>0 && !(i>=t_start && i<=t_end)) {
-                        t_pairs[j*2] = i;
-                        t_pairs[j*2+1] = ltoi[label_buf[i]];
-                        j++;
+            self.tie_pairs = np.empty(((np.logical_not(self._untie_)).sum(),2),dtype=np.uint32)
+            if self.tie_pairs.size>0:
+                try:
+                    from scipy import weave
+                    self._label_to_idx = np.zeros((self.tied_param.tie.max()+1,),dtype=np.int32)
+                    self._label_to_idx[self.tied_param.tie] = range(self.tied_param.size)
+                    ltoi = self._label_to_idx
+                    t_start=int(self.buf_idx[0])
+                    t_end=int(self.buf_idx[-1])
+                    label_buf = self.label_buf
+                    buf_size = self.label_buf.size
+                    t_pairs = self.tie_pairs
+                    code = """
+                    int j=0;
+                    for(int i=0;i<buf_size;i++) {
+                        if(label_buf[i]>0 && !(i>=t_start && i<=t_end)) {
+                            t_pairs[j*2] = i;
+                            t_pairs[j*2+1] = ltoi[label_buf[i]];
+                            j++;
+                        }
                     }
-                }
-                """
-                weave.inline(code, arg_names=['ltoi','t_start','t_end','label_buf','buf_size','t_pairs'])
-            except:
-                pass
+                    """
+                    weave.inline(code, arg_names=['ltoi','t_start','t_end','label_buf','buf_size','t_pairs'])
+                except:
+                    pass
             assert(np.all(self.tied_param.tie>0))
             
     def _keepParamList(self,plist):