diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/TerminologyCache.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/TerminologyCache.java
index 1a15235e9..9c6e1a790 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/TerminologyCache.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/context/TerminologyCache.java
@@ -414,7 +414,7 @@ public class TerminologyCache {
       for (ConceptSetFilterComponent f : cc.getFilter()) {
         if (!Utilities.noString(s))
           s = s + " & ";
-        s = s + f.getProperty()+" "+f.getOp().toCode()+" "+f.getValue();
+        s = s + f.getProperty()+" "+(f.hasOp() ? f.getOp().toCode() : "?")+" "+f.getValue();
       }
       return "from "+system+" where "+s+vsd;
     }