diff --git a/softwareconfiguration/hasco/src/main/java/hasco/core/HASCO.java b/softwareconfiguration/hasco/src/main/java/hasco/core/HASCO.java
index 1d2ed36e51..4c274a33f6 100644
--- a/softwareconfiguration/hasco/src/main/java/hasco/core/HASCO.java
+++ b/softwareconfiguration/hasco/src/main/java/hasco/core/HASCO.java
@@ -6,6 +6,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeoutException;
 import java.util.stream.Collectors;
 
@@ -74,7 +75,7 @@ public class HASCO<ISearch extends GraphSearchInput<N, A>, N, A, V extends Compa
 	private final List<HASCOSolutionCandidate<V>> listOfAllRecognizedSolutions = new ArrayList<>();
 	private int numUnparametrizedSolutions = -1;
 	private final Set<UnparametrizedComponentInstance> returnedUnparametrizedComponentInstances = new HashSet<>();
-	private Map<EvaluatedSearchSolutionCandidateFoundEvent<N, A, V>, HASCOSolutionEvent<V>> hascoSolutionEventCache = new HashMap<>();
+	private Map<EvaluatedSearchSolutionCandidateFoundEvent<N, A, V>, HASCOSolutionEvent<V>> hascoSolutionEventCache = new ConcurrentHashMap<>();
 
 	/* runtime variables of algorithm */
 	private final TimeRecordingEvaluationWrapper<V> timeGrabbingEvaluationWrapper;
@@ -168,6 +169,8 @@ public void receiveSearchEvent(final AlgorithmEvent event) {
 
 				@Subscribe
 				public void receiveSolutionCandidateFoundEvent(final EvaluatedSearchSolutionCandidateFoundEvent<N, A, V> solutionEvent) throws InterruptedException, TimeoutException, AlgorithmException {
+
+					System.err.println(Thread.currentThread().getName() + ": Received solution event in search listener " + solutionEvent);
 					EvaluatedSearchGraphPath<N, A, V> searchPath = solutionEvent.getSolutionCandidate();
 					Plan plan = HASCO.this.planningGraphGeneratorDeriver.getPlan(searchPath.getNodes());
 					ComponentInstance objectInstance = Util.getSolutionCompositionForPlan(HASCO.this.getInput().getComponents(), HASCO.this.planningProblem.getCorePlanningProblem().getInit(), plan, true);
@@ -190,6 +193,8 @@ public void receiveSolutionCandidateFoundEvent(final EvaluatedSearchSolutionCand
 					HASCO.this.updateBestSeenSolution(solution);
 					HASCO.this.listOfAllRecognizedSolutions.add(solution);
 					HASCOSolutionEvent<V> hascoSolutionEvent = new HASCOSolutionEvent<>(HASCO.this.getId(), solution);
+					HASCO.this.hascoSolutionEventCache.put(solutionEvent, hascoSolutionEvent);
+					System.err.println(Thread.currentThread().getName() + ": Post solution event in search listener " + solutionEvent);
 					HASCO.this.post(hascoSolutionEvent);
 				}
 
@@ -221,8 +226,12 @@ public void receiveSolutionCandidateFoundEvent(final EvaluatedSearchSolutionCand
 
 			/* otherwise, if a solution has been found, we announce this finding to our listeners and memorize if it is a new best candidate */
 			else if (searchEvent instanceof EvaluatedSearchSolutionCandidateFoundEvent) {
+				System.err.println(Thread.currentThread().getName() + ": Solution event in HASCO.nextWithException " + searchEvent);
 				HASCOSolutionEvent<V> hascoSolutionEvent = this.hascoSolutionEventCache.remove(searchEvent);
-				assert (hascoSolutionEvent != null) : "Hasco solution event has not been seen yet or cannot be retrieved from cache.";
+				assert (hascoSolutionEvent != null) : "Hasco solution event has not been seen yet or cannot be retrieved from cache. " + this.hascoSolutionEventCache;
+				if (hascoSolutionEvent == null) {
+					System.exit(0);
+				}
 				this.logger.info("Received new solution with score {} from search, communicating this solution to the HASCO listeners. Number of returned unparametrized solutions is now {}/{}.", hascoSolutionEvent.getScore(),
 						this.returnedUnparametrizedComponentInstances.size(), this.numUnparametrizedSolutions);
 				return hascoSolutionEvent;