diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 29df908..16dd4e4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,8 +36,9 @@ jobs:
           path: ~/.gradle/wrapper
           key: ${{ runner.os }}-gradle-wrapper-${{ hashFiles('**/gradle/wrapper/gradle-wrapper.properties') }}
       - name: Setup java
-        uses: actions/setup-java@v1
+        uses: actions/setup-java@v4
         with:
           java-version: ${{ matrix.java }}
+          distribution: 'temurin'
       - name: Build with gradle
         run: ./gradlew build
\ No newline at end of file
diff --git a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/SubmitStructureResponseBuilderV2_1.java b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/SubmitStructureResponseBuilderV2_1.java
index 7640105..ae5c82b 100644
--- a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/SubmitStructureResponseBuilderV2_1.java
+++ b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/SubmitStructureResponseBuilderV2_1.java
@@ -86,7 +86,9 @@ public RegistryInterfaceDocument buildSuccessResponse(SdmxBeans beans) throws Sd
         RegistryInterfaceType regInterface = responseType.addNewRegistryInterface();
         SubmitStructureResponseType returnType = regInterface.addNewSubmitStructureResponse();
 
-        regInterface.setHeader(headerXmlBeansBuilder.build(beans.getHeader()));
+        var headerType = headerXmlBeansBuilder.build(beans.getHeader());
+        V2_1Helper.ensureReceiverPresent(headerType);
+        regInterface.setHeader(headerType);
 
         processMaintainables(returnType, beans.getAllMaintainables());
         return responseType;
diff --git a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/V2_1Helper.java b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/V2_1Helper.java
index d1ad7a9..5f9278b 100644
--- a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/V2_1Helper.java
+++ b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/registry/response/impl/v21/V2_1Helper.java
@@ -101,4 +101,19 @@ public static void setHeader(BaseHeaderType header, SdmxBeans beans, String... r
         }
     }
 
+    /**
+     * RegistryInterfaceType.Header is typed as BasicHeaderType, which (unlike StructureHeaderType)
+     * requires exactly one Receiver. Callers building a registry request/response header from a
+     * caller-supplied HeaderBean must ensure one is present, since StructureHeaderXmlBeanBuilder
+     * no longer invents a default one.
+     *
+     * @param header the header to check and, if needed, patch with a default Receiver
+     */
+    public static void ensureReceiverPresent(BaseHeaderType header) {
+        if (!ObjectUtil.validCollection(header.getReceiverList())) {
+            PartyType receiver = header.addNewReceiver();
+            receiver.setId(HeaderHelper.INSTANCE.getReceiverId());
+        }
+    }
+
 }
diff --git a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/RegistrySubmitXmlBeanBuilder.java b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/RegistrySubmitXmlBeanBuilder.java
index 495cc79..d459b41 100644
--- a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/RegistrySubmitXmlBeanBuilder.java
+++ b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/RegistrySubmitXmlBeanBuilder.java
@@ -59,6 +59,7 @@ public RegistryInterfaceDocument build(SdmxBeans buildFrom) throws SdmxException
         BaseHeaderType headerType;
         if (buildFrom.getHeader() != null) {
             headerType = structureHeaderXmlBeanBuilder.build(buildFrom.getHeader());
+            V2_1Helper.ensureReceiverPresent(headerType);
             registryInterfaceType.setHeader(headerType);
         } else {
             headerType = registryInterfaceType.addNewHeader();
diff --git a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/StructureHeaderXmlBeanBuilder.java b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/StructureHeaderXmlBeanBuilder.java
index ad59a3c..6055391 100644
--- a/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/StructureHeaderXmlBeanBuilder.java
+++ b/SdmxStructureParser/src/main/java/org/sdmxsource/sdmx/structureparser/builder/xmlBeans/v21/StructureHeaderXmlBeanBuilder.java
@@ -60,8 +60,6 @@ public StructureHeaderType build(HeaderBean buildFrom) throws SdmxException {
             headerType.setPrepared(DateUtil.createCalendar(new Date()));
             SenderType senderType = headerType.addNewSender();
             senderType.setId("unknown");
-            PartyType receiverType = headerType.addNewReceiver();
-            receiverType.setId("unknown");
             return headerType;
         }
         if (ObjectUtil.validString(buildFrom.getId())) {
@@ -124,10 +122,6 @@ public StructureHeaderType build(HeaderBean buildFrom) throws SdmxException {
                 }
             }
         }
-        if (!ObjectUtil.validCollection(headerType.getReceiverList())) {
-            PartyType receiverType = headerType.addNewReceiver();
-            receiverType.setId("unknown");
-        }
         return headerType;
     }