diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java
index d60f239e5..d9bf4f934 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/ToolingExtensions.java
@@ -264,6 +264,7 @@ public class ToolingExtensions {
   public static final String EXT_ARTIFACT_NAME = "http://hl7.org/fhir/StructureDefinition/artifact-name";
   public static final String EXT_ARTIFACT_DESC = "http://hl7.org/fhir/StructureDefinition/artifact-description";  
   public static final String EXT_ED_SUPPRESS = "http://hl7.org/fhir/StructureDefinition/elementdefinition-suppress";
+  public static final String EXT_SEARCH_PARAMETER_BASE = "http://hl7.org/fhir/tools/StructureDefinition/searchparameter-base-type";;
   
   // specific extension helpers
 
diff --git a/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/instance/type/SearchParameterValidator.java b/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/instance/type/SearchParameterValidator.java
index a0f504d6b..f1ef96b09 100644
--- a/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/instance/type/SearchParameterValidator.java
+++ b/org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/instance/type/SearchParameterValidator.java
@@ -12,6 +12,7 @@ import org.hl7.fhir.r5.fhirpath.ExpressionNode.Kind;
 import org.hl7.fhir.r5.fhirpath.ExpressionNode.Operation;
 import org.hl7.fhir.r5.fhirpath.FHIRPathEngine.IssueMessage;
 import org.hl7.fhir.r5.model.SearchParameter;
+import org.hl7.fhir.r5.utils.ToolingExtensions;
 import org.hl7.fhir.utilities.Utilities;
 import org.hl7.fhir.utilities.i18n.I18nConstants;
 import org.hl7.fhir.utilities.validation.ValidationMessage;
@@ -45,9 +46,13 @@ public class SearchParameterValidator extends BaseValidator {
     if (cs.hasChild("expression", false)) {
       List<String> bases = new ArrayList<>();
       for (Element b : cs.getChildrenByName("base")) {
-        bases.add(b.primitiveValue());
+        if (b.hasExtension(ToolingExtensions.EXT_SEARCH_PARAMETER_BASE)) {
+          bases.add(b.getExtensionValue(ToolingExtensions.EXT_SEARCH_PARAMETER_BASE).primitiveValue());
+        } else {
+          bases.add(b.primitiveValue());
+        }
       }
-      if (!bases.isEmpty()) {
+      if (!bases.isEmpty()) { // that'd be an error somewhere else
         ok = checkExpression(errors, stack.push(cs.getNamedChild("expression", false), -1, null, null), cs.getNamedChildValue("expression", false), bases) && ok;
       }
     }