diff --git a/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java b/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java
index 5d37815c3f6faf2514926cdf1b3bae53ed6d5266..00496f14c1005a1f9c4a44da789d219660826fd8 100644
--- a/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java
+++ b/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java
@@ -37,6 +37,7 @@ import ch.systemsx.cisd.common.concurrent.ConcurrencyUtilities;
 import ch.systemsx.cisd.common.concurrent.FailureRecord;
 import ch.systemsx.cisd.common.concurrent.ITaskExecutor;
 import ch.systemsx.cisd.common.concurrent.ParallelizedExecutor;
+import ch.systemsx.cisd.common.exceptions.EnvironmentFailureException;
 import ch.systemsx.cisd.common.exceptions.Status;
 import ch.systemsx.cisd.common.filesystem.FileUtilities;
 import ch.systemsx.cisd.common.logging.LogCategory;
@@ -363,6 +364,12 @@ public class Hdf5ThumbnailGenerator implements IHDF5WriterClient
         }
 
         List<String> params = new ArrayList<String>();
+
+        if (convertUtilityOrNull == null)
+        {
+            throw new EnvironmentFailureException("Trying to generate thimbnails with ImageMagic, but 'convert' executable not found on the OS path.");
+        }
+
         params.addAll(Arrays.asList(convertUtilityOrNull.getPath(), imageFilePath, "-scale", size));
         List<String> additionalParams = thumbnailsStorageFormat.getImageMagicParams();
         if (additionalParams != null)