diff --git a/field.py b/field.py
index df37c9d..1ae057b 100644
--- a/field.py
+++ b/field.py
@@ -685,10 +685,12 @@ class BinaryFieldNd:
                 for source_ in np.unique(lab_hi[li]):
                     map_[source_] = 0
             else:
-                sl_lo = tuple(slice(0,1)     if ii==axis else slice(None) for ii in range(self._ndim))
-                sl_hi = tuple(slice(-1,None) if ii==axis else slice(None) for ii in range(self._ndim))
+                sl_lo  = tuple(slice(0,1)     if ii==axis else slice(None) for ii in range(self._ndim))
+                sl_hi  = tuple(slice(-1,None) if ii==axis else slice(None) for ii in range(self._ndim))
+                sl_pre = tuple(slice(-2,-1)   if ii==axis else slice(None) for ii in range(self._ndim))
                 lab_lo = labels_[sl_lo]
                 lab_hi = labels_[sl_hi]
+                lab_pre = np.unique(labels_[sl_pre]) # all labels in last (unwrapped) slice
                 # Initialize array to keep track of wrapping
                 wrap_[axis] = np.zeros(nlabels_+1,dtype=bool)
                 # Determine new label and map
@@ -703,12 +705,14 @@ class BinaryFieldNd:
                         while target_ != map_[target_]: # map it recursively
                             target_ = map_[target_]
                         map_[source_] = target_
-                        wrap_[axis][target_] = True
+                        if source_ in lab_pre: # check if source is not a ghost
+                            wrap_[axis][target_] = True
         # Remove gaps from target mapping
         idx_,map_ = np.unique(map_,return_index=True,return_inverse=True)[1:3]
         # Relabel and remove padding
         labels_  = map_[labels_[sl_pad]]
         nlabels_ = np.max(map_)
+        assert nlabels_==len(idx_)-1, "DEBUG assertion"
         for axis in range(self._ndim):
             if wrap_[axis] is not None:
                 wrap_[axis] = wrap_[axis][idx_]