diff --git a/modules/io/pymod/export_mmcif_io.cc b/modules/io/pymod/export_mmcif_io.cc
index d3213357183cf73841d9d1386e612b6e0828ca40..824d70340208f61ac9959cddcff4902833f1bed4 100644
--- a/modules/io/pymod/export_mmcif_io.cc
+++ b/modules/io/pymod/export_mmcif_io.cc
@@ -171,7 +171,8 @@ void export_mmcif_io()
   	.add_property("details", make_function(&MMCifInfoStructRefSeqDif::GetDetails, 
   				        return_value_policy<copy_const_reference>()))
   	.add_property("seq_rnum", &MMCifInfoStructRefSeqDif::GetSeqRNum)
-  	.add_property("db_rnum", &MMCifInfoStructRefSeqDif::GetDBRNum)
+    .add_property("db_rnum", make_function(&MMCifInfoStructRefSeqDif::GetDBRNum,
+                                           return_value_policy<copy_const_reference>()))
   ;
 
   typedef std::pair<int, int> IntPair;
diff --git a/modules/io/src/mol/mmcif_info.cc b/modules/io/src/mol/mmcif_info.cc
index e7f391894cab4e8ace515de79fa14f6e047fd683..e7d47078cc5ae4c9f3c4dabee23dd55c72dd12e1 100644
--- a/modules/io/src/mol/mmcif_info.cc
+++ b/modules/io/src/mol/mmcif_info.cc
@@ -168,7 +168,7 @@ MMCifInfoStructRef::GetAlignedSeq(const String& aid) const
 }
 
 MMCifInfoStructRefSeqDifPtr 
-MMCifInfoStructRefSeq::AddDif(int seq_rnum, int db_rnum, const String& details)
+MMCifInfoStructRefSeq::AddDif(int seq_rnum, const String& db_rnum, const String& details)
 {
 	MMCifInfoStructRefSeqDifPtr d(new MMCifInfoStructRefSeqDif(seq_rnum, db_rnum,
 				                                                     details));
diff --git a/modules/io/src/mol/mmcif_info.hh b/modules/io/src/mol/mmcif_info.hh
index 593fed6f2b70e25c777454bd3e8d95db8554ef56..ca8da62036b5151ff38cbefe65645515be2b0851 100644
--- a/modules/io/src/mol/mmcif_info.hh
+++ b/modules/io/src/mol/mmcif_info.hh
@@ -817,8 +817,8 @@ public:
   int GetSeqEnd() const { return seq_end_; }
   int GetDBBegin() const { return db_begin_; }
   int GetDBEnd() const { return db_end_; }
-  MMCifInfoStructRefSeqDifPtr AddDif(int seq_num, int db_num, 
-  		                               const String& details);
+  MMCifInfoStructRefSeqDifPtr AddDif(int seq_num, const String& db_rnum, 
+                                     const String& details);
   const std::vector<MMCifInfoStructRefSeqDifPtr>& GetDifs() const { return difs_; }
 private:
 	String   id_;
@@ -832,14 +832,14 @@ private:
 
 class DLLEXPORT_OST_IO MMCifInfoStructRefSeqDif {
 public:
-	MMCifInfoStructRefSeqDif(int seq_rnum, int db_rnum, const String& details): 
+	MMCifInfoStructRefSeqDif(int seq_rnum, const String& db_rnum, const String& details): 
 		seq_rnum_(seq_rnum), db_rnum_(db_rnum), details_(details) {}
 	int GetSeqRNum() const { return seq_rnum_;}
-	int GetDBRNum() const { return db_rnum_; }
+	const String& GetDBRNum() const { return db_rnum_; }
 	const String& GetDetails() const { return details_; }
 private:
 	int    seq_rnum_;
-	int    db_rnum_;
+	String db_rnum_;
 	String details_;
 };
 
diff --git a/modules/io/src/mol/mmcif_reader.cc b/modules/io/src/mol/mmcif_reader.cc
index b6d90fc756685626909edc2e6d6209ce07a557fd..93807f921e50c1457dc3cf7d0cc890375900183f 100644
--- a/modules/io/src/mol/mmcif_reader.cc
+++ b/modules/io/src/mol/mmcif_reader.cc
@@ -1542,33 +1542,30 @@ void MMCifReader::ParseStructRefSeq(const std::vector<StringRef>& columns)
 
 void MMCifReader::ParseStructRefSeqDif(const std::vector<StringRef>& columns)
 {
-	String aln_id=columns[indices_[SRSD_ALIGN_ID]].str();
-	std::pair<bool,int> db_rnum(true, -1);
-	if (!is_undef(columns[indices_[SRSD_DB_RNUM]])) {
-	  db_rnum=this->TryGetInt(columns[indices_[SRSD_DB_RNUM]],
-		    	                  "_struct_ref_seq_dif.pdbx_seq_db_seq_num",
-		                        profile_.fault_tolerant);
-	  
-	}
-	std::pair<bool,int> seq_rnum(true, -1);
-	if (!is_undef(columns[indices_[SRSD_SEQ_RNUM]])) {
-	  seq_rnum=this->TryGetInt(columns[indices_[SRSD_SEQ_RNUM]],
-		  	                     "_struct_ref_seq_dif.seq_num",
-			                       profile_.fault_tolerant);
-	  
-	}
-	if (!seq_rnum.first || !db_rnum.first) {
-		return;
-	}
+  String aln_id=columns[indices_[SRSD_ALIGN_ID]].str();
+  String db_rnum;
+  if (!is_undef(columns[indices_[SRSD_DB_RNUM]])) {
+    db_rnum=columns[indices_[SRSD_DB_RNUM]].str();
+  }
+  std::pair<bool,int> seq_rnum(true, -1);
+  if (!is_undef(columns[indices_[SRSD_SEQ_RNUM]])) {
+    seq_rnum=this->TryGetInt(columns[indices_[SRSD_SEQ_RNUM]],
+                             "_struct_ref_seq_dif.seq_num",
+                             profile_.fault_tolerant);
+    
+  }
+  if (!seq_rnum.first) {
+    return;
+  }
   String details;
   if (indices_[SRSD_DETAILS]!=-1) {
 	  details=columns[indices_[SRSD_DETAILS]].str();
-	}
-	bool found=false;
+  }
+  bool found=false;
   for (MMCifInfoStructRefs::iterator i=struct_refs_.begin(), 
  		  e=struct_refs_.end(); i!=e; ++i) { 
  	 if (MMCifInfoStructRefSeqPtr s=(*i)->GetAlignedSeq(aln_id)) {
-		 s->AddDif(seq_rnum.second, db_rnum.second, details); 
+		 s->AddDif(seq_rnum.second, db_rnum, details); 
 		 found=true;
  	 	 break;
  	 }