diff --git a/inema/wpint.py b/inema/wpint.py
index 37faa4b..95b4eee 100644
--- a/inema/wpint.py
+++ b/inema/wpint.py
@@ -214,6 +214,40 @@ class WarenpostInt(object):
             ret['contentPieceOrigin'] = origin_cc
         return ret
 
+    def shrink_contents_if_needed(self, contents):
+        """Attempt to shrink the number of content lines below the permitted 5. We
+           intentionally ignore the country of origin and group all lines by the
+           HTS code. All lines sharing the same HTS code are merged to one,
+           hopefully this is sufficient to get the count below 5."""
+        if len(contents) < 5:
+            return contents
+        # group items by HTS code
+        by_hts = {}
+        for c in contents:
+            hts = c['contentPieceHsCode'].strip()
+            if hts in by_hts:
+                by_hts[hts].append(c)
+            else:
+                by_hts[hts] = [c]
+        if len(by_hts.keys()) > 5:
+            raise ValueError('More than 5 distinct HTS numbers(%u); cannot merge' % (len(by_hts.keys())))
+        out = []
+        # generate one aggregate item per HTS code
+        for k in by_hts:
+            total_grams = 0
+            total_value = 0
+            total_qty = 0
+            for c in by_hts[k]:
+                total_grams += c['contentPieceNetweight']
+                total_value += float(c['contentPieceValue'])
+                total_qty += c['contentPieceAmount']
+            aggregate = by_hts[k][0]
+            aggregate['contentPieceAmount'] = total_qty
+            aggregate['contentPieceValue'] = "%.2f" % (total_value)
+            aggregate['contentPieceNetweight'] = total_grams
+            out.append(aggregate)
+        return out
+
     def build_item(self, product, sender, recipient, weight_grams, amount=0, currency='EUR',
                    shipment_nature='SALE_GOODS', customer_reference=None, contents=None):
         """Build an 'item' in the language of the WaPoInt API. Represents one shipment."""