diff --git a/CHANGELOG.md b/CHANGELOG.md
index 75d2a807c..8e2e6c883 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ Long run average computation via ValueIteration, LP based MDP model checking, pa
 - storm-cli-utilities now contains cli related stuff, instead of storm-lib
 - storm-pars: support for welldefinedness constraints in mdps.
 - symbolic (MT/BDD) bisimulation 
+- Fixed issue related to variable names that can not be used in Exprtk.
 
 ### Version 1.1.0 (2017/8)
 
diff --git a/src/storm/storage/dd/BisimulationDecomposition.cpp b/src/storm/storage/dd/BisimulationDecomposition.cpp
index 57190ff23..be19015ec 100644
--- a/src/storm/storage/dd/BisimulationDecomposition.cpp
+++ b/src/storm/storage/dd/BisimulationDecomposition.cpp
@@ -9,6 +9,9 @@
 #include "storm/models/symbolic/Mdp.h"
 #include "storm/models/symbolic/StandardRewardModel.h"
 
+#include "storm/settings/SettingsManager.h"
+#include "storm/settings/modules/IOSettings.h"
+
 #include "storm/utility/macros.h"
 #include "storm/exceptions/InvalidOperationException.h"
 #include "storm/exceptions/NotSupportedException.h"
@@ -29,16 +32,25 @@ namespace storm {
         
         template <storm::dd::DdType DdType, typename ValueType>
         BisimulationDecomposition<DdType, ValueType>::BisimulationDecomposition(storm::models::symbolic::Model<DdType, ValueType> const& model, storm::storage::BisimulationType const& bisimulationType) : model(model), preservationInformation(model, bisimulationType), refiner(createRefiner(model, Partition<DdType, ValueType>::create(model, bisimulationType, preservationInformation))) {
+            auto const& ioSettings = storm::settings::getModule<storm::settings::modules::IOSettings>();
+            showProgress = ioSettings.isExplorationShowProgressSet();
+            showProgressDelay = ioSettings.getExplorationShowProgressDelay();
             this->refineWrtRewardModels();
         }
         
         template <storm::dd::DdType DdType, typename ValueType>
         BisimulationDecomposition<DdType, ValueType>::BisimulationDecomposition(storm::models::symbolic::Model<DdType, ValueType> const& model, std::vector<std::shared_ptr<storm::logic::Formula const>> const& formulas, storm::storage::BisimulationType const& bisimulationType) : model(model), preservationInformation(model, formulas, bisimulationType), refiner(createRefiner(model, Partition<DdType, ValueType>::create(model, bisimulationType, preservationInformation))) {
+            auto const& ioSettings = storm::settings::getModule<storm::settings::modules::IOSettings>();
+            showProgress = ioSettings.isExplorationShowProgressSet();
+            showProgressDelay = ioSettings.getExplorationShowProgressDelay();
             this->refineWrtRewardModels();
         }
         
         template <storm::dd::DdType DdType, typename ValueType>
         BisimulationDecomposition<DdType, ValueType>::BisimulationDecomposition(storm::models::symbolic::Model<DdType, ValueType> const& model, Partition<DdType, ValueType> const& initialPartition, bisimulation::PreservationInformation<DdType, ValueType> const& preservationInformation) : model(model), preservationInformation(preservationInformation), refiner(createRefiner(model, initialPartition)) {
+            auto const& ioSettings = storm::settings::getModule<storm::settings::modules::IOSettings>();
+            showProgress = ioSettings.isExplorationShowProgressSet();
+            showProgressDelay = ioSettings.getExplorationShowProgressDelay();
             this->refineWrtRewardModels();
         }
         
@@ -55,12 +67,24 @@ namespace storm {
 #endif
 
             auto start = std::chrono::high_resolution_clock::now();
+            auto timeOfLastMessage = start;
             uint64_t iterations = 0;
             bool refined = true;
             while (refined) {
                 refined = refiner->refine(mode);
+
                 ++iterations;
                 STORM_LOG_TRACE("After iteration " << iterations << " partition has " << refiner->getStatePartition().getNumberOfBlocks() << " blocks.");
+                
+                if (showProgress) {
+                    auto now = std::chrono::high_resolution_clock::now();
+                    auto durationSinceLastMessage = std::chrono::duration_cast<std::chrono::seconds>(now - timeOfLastMessage).count();
+                    if (static_cast<uint64_t>(durationSinceLastMessage) >= showProgressDelay) {
+                        auto durationSinceStart = std::chrono::duration_cast<std::chrono::seconds>(now - start).count();
+                        std::cout << "State partition after " << iterations << " iterations (" << durationSinceStart << "ms) has " << refiner->getStatePartition().getNumberOfBlocks() << " blocks." << std::endl;
+                        timeOfLastMessage = std::chrono::high_resolution_clock::now();
+                    }
+                }
             }
             auto end = std::chrono::high_resolution_clock::now();
             
diff --git a/src/storm/storage/dd/BisimulationDecomposition.h b/src/storm/storage/dd/BisimulationDecomposition.h
index 66e562bea..2a62c9fa4 100644
--- a/src/storm/storage/dd/BisimulationDecomposition.h
+++ b/src/storm/storage/dd/BisimulationDecomposition.h
@@ -60,6 +60,12 @@ namespace storm {
             
             // The refiner to use.
             std::unique_ptr<bisimulation::PartitionRefiner<DdType, ValueType>> refiner;
+            
+            // A flag indicating whether progress is reported.
+            bool showProgress;
+            
+            // The delay between progress reports.
+            uint64_t showProgressDelay;
         };
         
     }
diff --git a/src/storm/storage/expressions/ExprtkExpressionEvaluator.cpp b/src/storm/storage/expressions/ExprtkExpressionEvaluator.cpp
index 42a405e49..70cd6e162 100755
--- a/src/storm/storage/expressions/ExprtkExpressionEvaluator.cpp
+++ b/src/storm/storage/expressions/ExprtkExpressionEvaluator.cpp
@@ -1,3 +1,5 @@
+#include <string>
+
 #include "storm/storage/expressions/ExprtkExpressionEvaluator.h"
 #include "storm/storage/expressions/ExpressionManager.h"
 
@@ -13,11 +15,11 @@ namespace storm {
 
             for (auto const& variableTypePair : manager) {
                 if (variableTypePair.second.isBooleanType()) {
-                    symbolTable->add_variable(variableTypePair.first.getName(), this->booleanValues[variableTypePair.first.getOffset()]);
+                    symbolTable->add_variable("v" + std::to_string(variableTypePair.first.getIndex()), this->booleanValues[variableTypePair.first.getOffset()]);
                 } else if (variableTypePair.second.isIntegerType()) {
-                    symbolTable->add_variable(variableTypePair.first.getName(), this->integerValues[variableTypePair.first.getOffset()]);
+                    symbolTable->add_variable("v" + std::to_string(variableTypePair.first.getIndex()), this->integerValues[variableTypePair.first.getOffset()]);
                 } else if (variableTypePair.second.isRationalType()) {
-                    symbolTable->add_variable(variableTypePair.first.getName(), this->rationalValues[variableTypePair.first.getOffset()]);
+                    symbolTable->add_variable("v" + std::to_string(variableTypePair.first.getIndex()), this->rationalValues[variableTypePair.first.getOffset()]);
                 }
             }
         }
diff --git a/src/storm/storage/expressions/ToExprtkStringVisitor.cpp b/src/storm/storage/expressions/ToExprtkStringVisitor.cpp
index e0326dd09..d9098af2b 100644
--- a/src/storm/storage/expressions/ToExprtkStringVisitor.cpp
+++ b/src/storm/storage/expressions/ToExprtkStringVisitor.cpp
@@ -167,7 +167,7 @@ namespace storm {
         }
         
         boost::any ToExprtkStringVisitor::visit(VariableExpression const& expression, boost::any const&) {
-            stream << expression.getVariableName();
+            stream << "v" + std::to_string(expression.getVariable().getIndex());
             return boost::any();
         }