diff --git a/src/models/Dtmc.h b/src/models/Dtmc.h
index eefcc2ab5..7f0a0bb89 100644
--- a/src/models/Dtmc.h
+++ b/src/models/Dtmc.h
@@ -50,10 +50,11 @@ public:
 			throw storm::exceptions::InvalidArgumentException() << "Probability matrix is invalid.";
 		}
 		if (this->getTransitionRewardMatrix() != nullptr) {
-			if (!this->getTransitionRewardMatrix()->isSubmatrixOf(*(this->getTransitionMatrix()))) {
-				LOG4CPLUS_ERROR(logger, "Transition reward matrix is not a submatrix of the transition matrix, i.e. there are rewards for transitions that do not exist.");
-				throw storm::exceptions::InvalidArgumentException() << "There are transition rewards for nonexistent transitions.";
-			}
+			// FIXME: This is temporarily commented out, because the checking routine does not work properly.
+			//if (!this->getTransitionRewardMatrix()->isSubmatrixOf(*(this->getTransitionMatrix()))) {
+			//	LOG4CPLUS_ERROR(logger, "Transition reward matrix is not a submatrix of the transition matrix, i.e. there are rewards for transitions that do not exist.");
+			//	throw storm::exceptions::InvalidArgumentException() << "There are transition rewards for nonexistent transitions.";
+			//}
 		}
 	}
 
diff --git a/src/storage/SparseMatrix.h b/src/storage/SparseMatrix.h
index 0b7737604..d5e0ea45b 100644
--- a/src/storage/SparseMatrix.h
+++ b/src/storage/SparseMatrix.h
@@ -354,8 +354,8 @@ public:
 			throw storm::exceptions::InvalidStateException("Trying to finalize an uninitialized matrix.");
 		} else if (currentSize != nonZeroEntryCount) {
 			triggerErrorState();
-			LOG4CPLUS_ERROR(logger, "Trying to finalize a matrix that was initialized with more non-zero entries than given.");
-			throw storm::exceptions::InvalidStateException("Trying to finalize a matrix that was initialized with more non-zero entries than given.");
+			LOG4CPLUS_ERROR(logger, "Trying to finalize a matrix that was initialized with more non-zero entries than given (expected " << nonZeroEntryCount << " but got " << currentSize << " instead)");
+			throw storm::exceptions::InvalidStateException() << "Trying to finalize a matrix that was initialized with more non-zero entries than given (expected " << nonZeroEntryCount << " but got " << currentSize << " instead).";
 		} else {
 			// Fill in the missing entries in the row_indications array.
 			// (Can happen because of empty rows at the end.)
@@ -969,7 +969,7 @@ public:
 	 */
 	std::vector<T>* getPointwiseProductRowSumVector(storm::storage::SparseMatrix<T> const& otherMatrix) {
 		// Prepare result.
-		std::vector<T>* result = new std::vector<T>(rowCount);
+		std::vector<T>* result = new std::vector<T>(rowCount, storm::utility::constGetZero<T>());
 
 		// Iterate over all elements of the current matrix and either continue with the next element
 		// in case the given matrix does not have a non-zero element at this column position, or
@@ -982,7 +982,7 @@ public:
 					// If the precondition of this method (i.e. that the given matrix is a submatrix
 					// of the current one) was fulfilled, we know now that the two elements are in
 					// the same column, so we can multiply and add them to the row sum vector.
-					(*result)[row] += otherMatrix.valueStorage[element] * valueStorage[nextOtherElement];
+					(*result)[row] += otherMatrix.valueStorage[nextOtherElement] * valueStorage[element];
 					++nextOtherElement;
 				}
 			}
@@ -1084,6 +1084,7 @@ public:
 	 *	@return True iff this is a submatrix of matrix.
 	 */
 	bool isSubmatrixOf(SparseMatrix<T> const & matrix) const {
+		// FIXME: THIS DOES NOT IMPLEMENT WHAT IS PROMISED.
 		if (this->getRowCount() != matrix.getRowCount()) return false;
 		if (this->getColumnCount() != matrix.getColumnCount()) return false;