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 160bfd11e..2d05f10dd 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
@@ -25,6 +25,7 @@ import java.io.OutputStream;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Comparator;
+import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -66,6 +67,7 @@ import org.hl7.fhir.r5.model.ElementDefinition.TypeRefComponent;
 import org.hl7.fhir.r5.model.Enumeration;
 import org.hl7.fhir.r5.model.Enumerations.BindingStrength;
 import org.hl7.fhir.r5.model.Enumerations.FHIRVersion;
+import org.hl7.fhir.r5.model.Enumerations.PublicationStatus;
 import org.hl7.fhir.r5.model.Extension;
 import org.hl7.fhir.r5.model.IdType;
 import org.hl7.fhir.r5.model.IntegerType;
@@ -5218,6 +5220,36 @@ public class ProfileUtilities extends TranslatingUtilities {
   }
 
 
+  public static StructureDefinition makeBaseDefinition(FHIRVersion fhirVersion) {
+    StructureDefinition base = new StructureDefinition();
+    base.setId("Base");
+    base.setUrl("http://hl7.org/fhir/StructureDefinition/Base");
+    base.setVersion(fhirVersion.toCode());
+    base.setName("Base"); 
+    base.setStatus(PublicationStatus.ACTIVE);
+    base.setDate(new Date());
+    base.setFhirVersion(fhirVersion);
+    base.setKind(StructureDefinitionKind.COMPLEXTYPE); 
+    base.setAbstract(true); 
+    base.setType("Base");
+    ElementDefinition e = base.getSnapshot().getElementFirstRep();
+    e.setId("Base");
+    e.setPath("Base"); 
+    e.setMin(0); 
+    e.setMax("*"); 
+    e.getBase().setPath("Base");
+    e.getBase().setMin(0); 
+    e.getBase().setMax("*"); 
+    e.setIsModifier(false); 
+    e = base.getDifferential().getElementFirstRep();
+    e.setId("Base");
+    e.setPath("Base"); 
+    e.setMin(0); 
+    e.setMax("*"); 
+    return base;
+  }
+
+
 
   
 }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/SimpleWorkerContext.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/SimpleWorkerContext.java
index b9be02d21..725a08b74 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/SimpleWorkerContext.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/SimpleWorkerContext.java
@@ -594,17 +594,27 @@ public class SimpleWorkerContext extends BaseWorkerContext implements IWorkerCon
   }
   
   public void generateSnapshot(StructureDefinition p) throws DefinitionException, FHIRException {
-    if (!p.hasSnapshot() && p.getKind() != StructureDefinitionKind.LOGICAL) {
+    generateSnapshot(p, false);
+  }
+  
+  public void generateSnapshot(StructureDefinition p, boolean logical) throws DefinitionException, FHIRException {
+    if (!p.hasSnapshot() && (logical || p.getKind() != StructureDefinitionKind.LOGICAL)) {
       if (!p.hasBaseDefinition())
         throw new DefinitionException("Profile "+p.getName()+" ("+p.getUrl()+") has no base and no snapshot");
       StructureDefinition sd = fetchResource(StructureDefinition.class, p.getBaseDefinition());
-      if (sd == null)
+      if (sd == null && "http://hl7.org/fhir/StructureDefinition/Base".equals(p.getBaseDefinition())) {
+        sd = ProfileUtilities.makeBaseDefinition(p.getFhirVersion());
+      }
+      if (sd == null) {
         throw new DefinitionException("Profile "+p.getName()+" ("+p.getUrl()+") base "+p.getBaseDefinition()+" could not be resolved");
+      }
       List<ValidationMessage> msgs = new ArrayList<ValidationMessage>();
       List<String> errors = new ArrayList<String>();
       ProfileUtilities pu = new ProfileUtilities(this, msgs, this);
       pu.setThrowException(false);
-      pu.sortDifferential(sd, p, p.getUrl(), errors);
+      if (sd.getDerivation() == TypeDerivationRule.CONSTRAINT) {
+        pu.sortDifferential(sd, p, p.getUrl(), errors);
+      }
       pu.setDebug(false);
       for (String err : errors)
         msgs.add(new ValidationMessage(Source.ProfileValidator, IssueType.EXCEPTION, p.getUserString("path"), "Error sorting Differential: "+err, ValidationMessage.IssueSeverity.ERROR));