diff --git a/src/main/java/org/spdx/library/model/ExternalDocumentRef.java b/src/main/java/org/spdx/library/model/ExternalDocumentRef.java
index 49adef13..a29f56cc 100644
--- a/src/main/java/org/spdx/library/model/ExternalDocumentRef.java
+++ b/src/main/java/org/spdx/library/model/ExternalDocumentRef.java
@@ -183,7 +183,7 @@ public ExternalDocumentRef setChecksum(Checksum checksum) throws InvalidSPDXAnal
 	 * @return the spdxDocumentNamespace or empty string if no namespace
 	 */
 	public String getSpdxDocumentNamespace() throws InvalidSPDXAnalysisException {
-		Optional<Object> docNamespace = getObjectPropertyValue(SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT);
+		Optional<Object> docNamespace = getModelStore().getValue(getDocumentUri(), getId(), SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT);
 		if (!docNamespace.isPresent()) {
 			logger.warn("SPDX document namespace not found");
 			return "";
diff --git a/src/main/java/org/spdx/library/model/ExternalSpdxElement.java b/src/main/java/org/spdx/library/model/ExternalSpdxElement.java
index 0439c4ab..4a210db6 100644
--- a/src/main/java/org/spdx/library/model/ExternalSpdxElement.java
+++ b/src/main/java/org/spdx/library/model/ExternalSpdxElement.java
@@ -196,8 +196,8 @@ public static ExternalSpdxElement uriToExternalSpdxElement(String uri,
 	
 	public static String externalDocumentIdToNamespace(String externalDocumentId,
 			IModelStore stModelStore, String stDocumentUri, ModelCopyManager copyManager) throws InvalidSPDXAnalysisException {
-		Optional<Object> retval = getObjectPropertyValue(stModelStore, stDocumentUri, 
-				externalDocumentId, SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT, copyManager);
+
+		Optional<Object> retval = stModelStore.getValue(stDocumentUri, externalDocumentId, SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT);
 		if (!retval.isPresent()) {
 			throw new InvalidSPDXAnalysisException("No external document reference exists for document ID "+externalDocumentId);
 		}