diff --git a/src/map/IMG/deltastream.cpp b/src/map/IMG/deltastream.cpp
index 9c07efca..7bb396af 100644
--- a/src/map/IMG/deltastream.cpp
+++ b/src/map/IMG/deltastream.cpp
@@ -1,6 +1,5 @@
 #include "deltastream.h"
 
-
 using namespace IMG;
 
 static int bitSize(quint8 baseSize, bool variableSign, bool extraBit)
@@ -19,21 +18,21 @@ static int bitSize(quint8 baseSize, bool variableSign, bool extraBit)
 	return bits;
 }
 
-DeltaStream::DeltaStream(const SubFile &file, SubFile::Handle &hdl,
-  quint32 length, quint8 info, bool extraBit, bool extended)
-  : BitStream1(file, hdl, length), _readBits(0xFFFFFFFF)
+bool DeltaStream::init(quint8 info, bool extraBit, bool extended)
 {
 	_extraBit = extraBit ? 1 : 0;
 	if (!(sign(_lonSign) && sign(_latSign)))
-		return;
+		return false;
 	if (extended) {
 		quint32 b;
 		if (!read(1, b))
-			return;
+			return false;
 	}
 	_lonBits = bitSize(info & 0x0F, !_lonSign, extraBit);
 	_latBits = bitSize(info >> 4, !_latSign, false);
 	_readBits = _lonBits + _latBits;
+
+	return true;
 }
 
 bool DeltaStream::readDelta(int bits, int sign, int extraBit,
diff --git a/src/map/IMG/deltastream.h b/src/map/IMG/deltastream.h
index 4e698857..d4deecdf 100644
--- a/src/map/IMG/deltastream.h
+++ b/src/map/IMG/deltastream.h
@@ -7,9 +7,10 @@ namespace IMG {
 
 class DeltaStream : public BitStream1 {
 public:
-	DeltaStream(const SubFile &file, SubFile::Handle &hdl, quint32 length,
-	  quint8 info, bool extraBit, bool extended);
+	DeltaStream(const SubFile &file, SubFile::Handle &hdl, quint32 length)
+	  : BitStream1(file, hdl, length), _readBits(0xFFFFFFFF) {}
 
+	bool init(quint8 info, bool extraBit, bool extended);
 	bool readNext(qint32 &lonDelta, qint32 &latDelta)
 	{
 		return hasNext()
diff --git a/src/map/IMG/rgnfile.cpp b/src/map/IMG/rgnfile.cpp
index deacae64..bfd93fdb 100644
--- a/src/map/IMG/rgnfile.cpp
+++ b/src/map/IMG/rgnfile.cpp
@@ -218,8 +218,9 @@ bool RGNFile::polyObjects(Handle &hdl, const SubDiv *subdiv,
 		poly.points.append(QPointF(c.lon(), c.lat()));
 
 		qint32 lonDelta, latDelta;
-		DeltaStream stream(*this, hdl, len, bitstreamInfo, labelPtr & 0x400000,
-		  false);
+		DeltaStream stream(*this, hdl, len);
+		if (!stream.init(bitstreamInfo, labelPtr & 0x400000, false))
+			return false;
 		while (stream.readNext(lonDelta, latDelta)) {
 			pos.rx() += LS(lonDelta, (24-subdiv->bits()));
 			if (pos.rx() >= 0x800000 && subdiv->lon() >= 0)
@@ -325,8 +326,9 @@ bool RGNFile::extPolyObjects(Handle &hdl, const SubDiv *subdiv, quint32 shift,
 				return false;
 
 			qint32 lonDelta, latDelta;
-			DeltaStream stream(*this, hdl, len - 1, bitstreamInfo, false, true);
-
+			DeltaStream stream(*this, hdl, len - 1);
+			if (!stream.init(bitstreamInfo, false, true))
+				return false;
 			while (stream.readNext(lonDelta, latDelta)) {
 				pos.rx() += LS(lonDelta, 24-subdiv->bits());
 				if (pos.rx() >= 0x800000 && subdiv->lon() >= 0)