diff --git a/code/ColladaParser.cpp b/code/ColladaParser.cpp
index 41aaee320..2f7787b62 100644
--- a/code/ColladaParser.cpp
+++ b/code/ColladaParser.cpp
@@ -599,7 +599,7 @@ void ColladaParser::ReadControllerWeights( Collada::Controller& pController)
 		if( mReader->getNodeType() == irr::io::EXN_ELEMENT) 
 		{
 			// Input channels for weight data. Two possible semantics: "JOINT" and "WEIGHT"
-			if( IsElement( "input"))
+			if( IsElement( "input") && vertexCount > 0 )
 			{
 				InputChannel channel;
 
@@ -628,7 +628,7 @@ void ColladaParser::ReadControllerWeights( Collada::Controller& pController)
 				if( !mReader->isEmptyElement())
 					SkipElement();
 			}
-			else if( IsElement( "vcount"))
+			else if( IsElement( "vcount") && vertexCount > 0 )
 			{
 				// read weight count per vertex
 				const char* text = GetTextContent();
@@ -648,7 +648,7 @@ void ColladaParser::ReadControllerWeights( Collada::Controller& pController)
 				// reserve weight count 
 				pController.mWeights.resize( numWeights);
 			}
-			else if( IsElement( "v"))
+			else if( IsElement( "v") && vertexCount > 0 )
 			{
 				// read JointIndex - WeightIndex pairs
 				const char* text = GetTextContent();
@@ -1656,6 +1656,7 @@ void ColladaParser::ReadDataArray()
 	std::string id = mReader->getAttributeValue( indexID);
 	int indexCount = GetAttribute( "count");
 	unsigned int count = (unsigned int) mReader->getAttributeValueAsInt( indexCount);
+	if (count == 0) { return; } // some exporters write empty data arrays with count="0"
 	const char* content = TestTextContent();
 
   // read values and store inside an array in the data library
diff --git a/include/assimp/quaternion.inl b/include/assimp/quaternion.inl
index b6394b8a3..9113848b8 100644
--- a/include/assimp/quaternion.inl
+++ b/include/assimp/quaternion.inl
@@ -69,12 +69,12 @@ bool aiQuaterniont<TReal>::operator!= (const aiQuaterniont& o) const
 template<typename TReal>
 inline aiQuaterniont<TReal>::aiQuaterniont( const aiMatrix3x3t<TReal> &pRotMatrix)
 {
-	TReal t = 1 + pRotMatrix.a1 + pRotMatrix.b2 + pRotMatrix.c3;
+	TReal t = pRotMatrix.a1 + pRotMatrix.b2 + pRotMatrix.c3;
 
 	// large enough
-	if( t > static_cast<TReal>(0.001))
+	if( t > static_cast<TReal>(0))
 	{
-		TReal s = sqrt( t) * static_cast<TReal>(2.0);
+		TReal s = sqrt(1 + t) * static_cast<TReal>(2.0);
 		x = (pRotMatrix.c2 - pRotMatrix.b3) / s;
 		y = (pRotMatrix.a3 - pRotMatrix.c1) / s;
 		z = (pRotMatrix.b1 - pRotMatrix.a2) / s;