diff --git a/src/storm-pomdp/transformer/MakeStateSetObservationClosed.cpp b/src/storm-pomdp/transformer/MakeStateSetObservationClosed.cpp
new file mode 100644
index 000000000..ce23358f6
--- /dev/null
+++ b/src/storm-pomdp/transformer/MakeStateSetObservationClosed.cpp
@@ -0,0 +1,70 @@
+#include "storm-pomdp/transformer/MakeStateSetObservationClosed.h"
+
+
+namespace storm {
+    namespace transformer {
+        
+        template<typename ValueType>
+        MakeStateSetObservationClosed<ValueType>::MakeStateSetObservationClosed(std::shared_ptr<storm::models::sparse::Pomdp<ValueType>> pomdp) : pomdp(pomdp) { }
+        
+        template<typename ValueType>
+        std::pair<std::shared_ptr<storm::models::sparse::Pomdp<ValueType>>, std::set<uint32_t>> MakeStateSetObservationClosed<ValueType>::transform(storm::storage::BitVector const& stateSet) const {
+            // Collect observations of target states
+            std::set<uint32_t> oldObservations;
+            for (auto const& state : stateSet) {
+                oldObservations.insert(pomdp->getObservation(state));
+            }
+            
+            // Collect observations that belong to both, target states and non-target states.
+            // Add a fresh observation for each of them
+            std::map<uint32_t, uint32_t> oldToNewObservationMap;
+            uint32_t freshObs = pomdp->getNrObservations();
+            for (uint64_t state = stateSet.getNextUnsetIndex(0); state < stateSet.size(); state = stateSet.getNextUnsetIndex(state + 1)) {
+                uint32_t obs = pomdp->getObservation(state);
+                if (oldObservations.count(obs) > 0) {
+                    // this observation belongs to both, target and non-target states.
+                    if (oldToNewObservationMap.emplace(obs, freshObs).second) {
+                        // We actually inserted something, i.e., we have not seen this observation before.
+                        // For the next observation (that is different from obs) we want to insert another fresh observation index
+                        // This is to preserve the assumption that states with the same observation have the same enabled actions.
+                        ++freshObs;
+                    }
+                }
+            }
+            
+            // Check whether the state set already is observation closed.
+            if (oldToNewObservationMap.empty()) {
+                return {pomdp, std::move(oldObservations)};
+            } else {
+                // Create new observations
+                auto newObservationVector = pomdp->getObservations();
+                for (auto const& state : stateSet) {
+                    auto findRes = oldToNewObservationMap.find(pomdp->getObservation(state));
+                    if (findRes != oldToNewObservationMap.end()) {
+                        newObservationVector[state] = findRes->second;
+                    }
+                }
+                // Create a copy of the pomdp and change observations accordingly.
+                // This transformation preserves canonicity.
+                auto transformed = std::make_shared<storm::models::sparse::Pomdp<ValueType>>(*pomdp);
+                transformed->updateObservations(std::move(newObservationVector), true);
+                
+                // Finally, get the new set of target observations
+                std::set<uint32_t> newObservations;
+                for (auto const& obs : oldObservations) {
+                    auto findRes = oldToNewObservationMap.find(obs);
+                    if (findRes == oldToNewObservationMap.end()) {
+                        newObservations.insert(obs);
+                    } else {
+                        newObservations.insert(findRes->second);
+                    }
+                }
+                
+                return {transformed, std::move(newObservations)};
+            }
+        }
+        
+        template class MakeStateSetObservationClosed<double>;
+        template class MakeStateSetObservationClosed<storm::RationalNumber>;
+    }
+}
\ No newline at end of file
diff --git a/src/storm-pomdp/transformer/MakeStateSetObservationClosed.h b/src/storm-pomdp/transformer/MakeStateSetObservationClosed.h
new file mode 100644
index 000000000..4a7f20c92
--- /dev/null
+++ b/src/storm-pomdp/transformer/MakeStateSetObservationClosed.h
@@ -0,0 +1,26 @@
+#pragma once
+#include <memory>
+
+#include "storm/models/sparse/Pomdp.h"
+namespace storm {
+    namespace transformer {
+
+        template<typename ValueType>
+        class MakeStateSetObservationClosed {
+
+        public:
+            MakeStateSetObservationClosed(std::shared_ptr<storm::models::sparse::Pomdp<ValueType>> pomdp);
+            
+            /*!
+             * Ensures that the given set of states is observation closed, potentially, adding new observation(s)
+             * A set of states S is observation closed, iff there is a set of observations Z such that `o(s) in Z iff s in S`
+             *
+             * @return the model where the given set of states is observation closed as well as the set of observations that uniquely describe the given state set.
+             *      If the state set is already observation close, we return the original POMDP, i.e., the pomdp is not copied.
+             */
+            std::pair<std::shared_ptr<storm::models::sparse::Pomdp<ValueType>>, std::set<uint32_t>> transform(storm::storage::BitVector const& stateSet) const;
+        protected:
+            std::shared_ptr<storm::models::sparse::Pomdp<ValueType>> pomdp;
+        };
+    }
+}
\ No newline at end of file
diff --git a/src/storm/models/sparse/Pomdp.cpp b/src/storm/models/sparse/Pomdp.cpp
index b38b3dd2f..dc5461120 100644
--- a/src/storm/models/sparse/Pomdp.cpp
+++ b/src/storm/models/sparse/Pomdp.cpp
@@ -75,6 +75,12 @@ namespace storm {
                 return observations;
             }
             
+            template<typename ValueType, typename RewardModelType>
+            void Pomdp<ValueType, RewardModelType>::updateObservations(std::vector<uint32_t>&& newObservations, bool preservesCanonicity) {
+                observations = std::move(newObservations);
+                computeNrObservations();
+                setIsCanonic(isCanonic() && preservesCanonicity);
+            }
 
             template<typename ValueType, typename RewardModelType>
             std::string Pomdp<ValueType, RewardModelType>::additionalDotStateInfo(uint64_t state) const {
diff --git a/src/storm/models/sparse/Pomdp.h b/src/storm/models/sparse/Pomdp.h
index 408b2dec7..cacee0953 100644
--- a/src/storm/models/sparse/Pomdp.h
+++ b/src/storm/models/sparse/Pomdp.h
@@ -65,6 +65,16 @@ namespace storm {
                 uint64_t getMaxNrStatesWithSameObservation() const;
                 
                 std::vector<uint32_t> const& getObservations() const;
+                
+                /*!
+                 * Changes the observations to the given ones and updates redundant informations (like the number of observations)
+                 * After calling this method, isCanonic() returns true iff (i) isCanonic() returned true before calling this method and (ii) preservesCanonicity was set to true.
+                 *
+                 * @param newObservations The new observations
+                 * @param preservesCanonicity specifies whether the pomdp is still canonic (assuming that it was canonic before)
+                 *
+                 */
+                void updateObservations(std::vector<uint32_t>&& newObservations, bool preservesCanonicity);
 
                 std::vector<uint64_t> getStatesWithObservation(uint32_t observation) const;