diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/conformance/ProfileUtilities.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/conformance/ProfileUtilities.java
index e86086ac1..25106f617 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/conformance/ProfileUtilities.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/conformance/ProfileUtilities.java
@@ -408,55 +408,60 @@ public class ProfileUtilities extends TranslatingUtilities {
 
     derived.setSnapshot(new StructureDefinitionSnapshotComponent());
 
-    
-    // so we have two lists - the base list, and the differential list
-    // the differential list is only allowed to include things that are in the base list, but
-    // is allowed to include them multiple times - thereby slicing them
+    try {
+      // so we have two lists - the base list, and the differential list
+      // the differential list is only allowed to include things that are in the base list, but
+      // is allowed to include them multiple times - thereby slicing them
 
-    // our approach is to walk through the base list, and see whether the differential
-    // says anything about them.
-    int baseCursor = 0;
-    int diffCursor = 0; // we need a diff cursor because we can only look ahead, in the bound scoped by longer paths
+      // our approach is to walk through the base list, and see whether the differential
+      // says anything about them.
+      int baseCursor = 0;
+      int diffCursor = 0; // we need a diff cursor because we can only look ahead, in the bound scoped by longer paths
 
-    if (derived.hasDifferential() && !derived.getDifferential().getElementFirstRep().getPath().contains(".") && !derived.getDifferential().getElementFirstRep().getType().isEmpty())
-      throw new Error("type on first differential element!");
+      if (derived.hasDifferential() && !derived.getDifferential().getElementFirstRep().getPath().contains(".") && !derived.getDifferential().getElementFirstRep().getType().isEmpty())
+        throw new Error("type on first differential element!");
 
-    for (ElementDefinition e : derived.getDifferential().getElement()) 
-      e.clearUserData(GENERATED_IN_SNAPSHOT);
-    
-    // we actually delegate the work to a subroutine so we can re-enter it with a different cursors
+      for (ElementDefinition e : derived.getDifferential().getElement()) 
+        e.clearUserData(GENERATED_IN_SNAPSHOT);
 
-    processPaths("", derived.getSnapshot(), base.getSnapshot(), derived.getDifferential(), baseCursor, diffCursor, base.getSnapshot().getElement().size()-1, 
-        derived.getDifferential().hasElement() ? derived.getDifferential().getElement().size()-1 : -1, url, webUrl, derived.getId(), null, null, false, base.getUrl(), null, false, new ArrayList<ElementRedirection>());
-    if (!derived.getSnapshot().getElementFirstRep().getType().isEmpty())
-      throw new Error("type on first snapshot element for "+derived.getSnapshot().getElementFirstRep().getPath()+" in "+derived.getUrl()+" from "+base.getUrl());
-    updateMaps(base, derived);
-    setIds(derived, false);
-    
-    if (DEBUG) {
-      System.out.println("Differential: ");
-      for (ElementDefinition ed : derived.getDifferential().getElement())
-        System.out.println("  "+ed.getPath()+" : "+typeSummaryWithProfile(ed)+"["+ed.getMin()+".."+ed.getMax()+"]"+sliceSummary(ed)+"  id = "+ed.getId()+" "+constraintSummary(ed));
-      System.out.println("Snapshot: ");
-      for (ElementDefinition ed : derived.getSnapshot().getElement())
-        System.out.println("  "+ed.getPath()+" : "+typeSummaryWithProfile(ed)+"["+ed.getMin()+".."+ed.getMax()+"]"+sliceSummary(ed)+"  id = "+ed.getId()+" "+constraintSummary(ed));
-    }
-    //Check that all differential elements have a corresponding snapshot element
-    for (ElementDefinition e : derived.getDifferential().getElement()) {
-      if (!e.hasUserData(GENERATED_IN_SNAPSHOT)) {
-        System.out.println("Error in snapshot generation: Differential for "+derived.getUrl()+" with id: " + e.getId()+" has an element that is not marked with a snapshot match");
-        if (exception)
-          throw new DefinitionException("Snapshot for "+derived.getUrl()+" does not contain an element that matches an existing differential element that has id: " + e.getId());
-        else
-          messages.add(new ValidationMessage(Source.ProfileValidator, ValidationMessage.IssueType.VALUE, url, "Snapshot for "+derived.getUrl()+" does not contain an element that matches an existing differential element that has id: " + e.getId(), ValidationMessage.IssueSeverity.ERROR));
+      // we actually delegate the work to a subroutine so we can re-enter it with a different cursors
+
+      processPaths("", derived.getSnapshot(), base.getSnapshot(), derived.getDifferential(), baseCursor, diffCursor, base.getSnapshot().getElement().size()-1, 
+          derived.getDifferential().hasElement() ? derived.getDifferential().getElement().size()-1 : -1, url, webUrl, derived.getId(), null, null, false, base.getUrl(), null, false, new ArrayList<ElementRedirection>());
+      if (!derived.getSnapshot().getElementFirstRep().getType().isEmpty())
+        throw new Error("type on first snapshot element for "+derived.getSnapshot().getElementFirstRep().getPath()+" in "+derived.getUrl()+" from "+base.getUrl());
+      updateMaps(base, derived);
+      setIds(derived, false);
+
+      if (DEBUG) {
+        System.out.println("Differential: ");
+        for (ElementDefinition ed : derived.getDifferential().getElement())
+          System.out.println("  "+ed.getPath()+" : "+typeSummaryWithProfile(ed)+"["+ed.getMin()+".."+ed.getMax()+"]"+sliceSummary(ed)+"  id = "+ed.getId()+" "+constraintSummary(ed));
+        System.out.println("Snapshot: ");
+        for (ElementDefinition ed : derived.getSnapshot().getElement())
+          System.out.println("  "+ed.getPath()+" : "+typeSummaryWithProfile(ed)+"["+ed.getMin()+".."+ed.getMax()+"]"+sliceSummary(ed)+"  id = "+ed.getId()+" "+constraintSummary(ed));
       }
-    }
-    if (derived.getDerivation() == TypeDerivationRule.SPECIALIZATION) {
-      for (ElementDefinition ed : derived.getSnapshot().getElement()) {
-        if (!ed.hasBase()) {
-          ed.getBase().setPath(ed.getPath()).setMin(ed.getMin()).setMax(ed.getMax());
+      //Check that all differential elements have a corresponding snapshot element
+      for (ElementDefinition e : derived.getDifferential().getElement()) {
+        if (!e.hasUserData(GENERATED_IN_SNAPSHOT)) {
+          System.out.println("Error in snapshot generation: Differential for "+derived.getUrl()+" with id: " + e.getId()+" has an element that is not marked with a snapshot match");
+          if (exception)
+            throw new DefinitionException("Snapshot for "+derived.getUrl()+" does not contain an element that matches an existing differential element that has id: " + e.getId());
+          else
+            messages.add(new ValidationMessage(Source.ProfileValidator, ValidationMessage.IssueType.VALUE, url, "Snapshot for "+derived.getUrl()+" does not contain an element that matches an existing differential element that has id: " + e.getId(), ValidationMessage.IssueSeverity.ERROR));
         }
       }
+      if (derived.getDerivation() == TypeDerivationRule.SPECIALIZATION) {
+        for (ElementDefinition ed : derived.getSnapshot().getElement()) {
+          if (!ed.hasBase()) {
+            ed.getBase().setPath(ed.getPath()).setMin(ed.getMin()).setMax(ed.getMax());
+          }
+        }
+      }
+    } catch (Exception e) {
+      // if we had an exception generating the snapshot, make sure we don't leave any half generated snapshot behind
+      derived.setSnapshot(null);
+      throw e;
     }
   }