diff --git a/src/map/IMG/huffmantable.cpp b/src/map/IMG/huffmantable.cpp
index cbee4831..851c3392 100644
--- a/src/map/IMG/huffmantable.cpp
+++ b/src/map/IMG/huffmantable.cpp
@@ -33,7 +33,7 @@ bool HuffmanTable::load(const RGNFile *rgn, SubFile::Handle &rgnHdl)
 	_aclTable = _bsrchTable + _bsrchEntryBytes * _bsrchEntries;
 	_huffmanTable = _aclTable + (_aclEntryBytes << _aclBits);
 
-	return (_symBits <= 32 && _symbolBits <= 32);
+	return (_symBits > 0 && _symBits <= 32 && _symbolBits <= 32);
 }
 
 quint32 HuffmanTable::symbol(quint32 data, quint8 &size) const
diff --git a/src/map/hillshading.cpp b/src/map/hillshading.cpp
index 66baf8f5..4d0a921e 100644
--- a/src/map/hillshading.cpp
+++ b/src/map/hillshading.cpp
@@ -78,6 +78,8 @@ QImage HillShading::render(const MatrixD &m, int extend)
 
 	getConstants(_azimuth, _altitude, c);
 
+	Q_ASSERT(extend > 0);
+
 	for (int y = extend; y < m.h() - extend; y++) {
 		for (int x = extend; x < m.w() - extend; x++) {
 			getSubmatrix(x, y, m, sm);