diff --git a/src/copy/pvCopy.cpp b/src/copy/pvCopy.cpp
index 7694ecf..0916878 100644
--- a/src/copy/pvCopy.cpp
+++ b/src/copy/pvCopy.cpp
@@ -432,6 +432,7 @@ bool PVCopy::init(epics::pvData::PVStructurePtr const &pvRequest)
     PVStructurePtr pvMasterStructure = pvMaster;
     size_t len = pvRequest->getPVFields().size();
     bool entireMaster = false;
+    requestHasMasterField = false;
     PVStructurePtr pvOptions;
     if(len==0) {
         entireMaster = true;
@@ -441,6 +442,9 @@ bool PVCopy::init(epics::pvData::PVStructurePtr const &pvRequest)
         // then assume the top level PV structure is requested
         PVStructurePtr masterFieldPtr = pvMaster->getSubField<PVStructure>("_");
         PVStructurePtr requestFieldPtr = pvRequest->getSubField<PVStructure>("_");
+        if (requestFieldPtr) {
+            requestHasMasterField = true;
+        }
         if (!masterFieldPtr && requestFieldPtr) {
             entireMaster = true;
             pvOptions = requestFieldPtr->getSubField<PVStructure>("_options");
diff --git a/src/pv/pvStructureCopy.h b/src/pv/pvStructureCopy.h
index 3ae37a3..8bce170 100644
--- a/src/pv/pvStructureCopy.h
+++ b/src/pv/pvStructureCopy.h
@@ -167,6 +167,10 @@ public:
      *  name is the subField name and value is the subField value.
      */
     epics::pvData::PVStructurePtr getOptions(std::size_t fieldOffset);
+    /**
+     * Is master field requested?
+     */
+    bool isMasterFieldRequested() const {return requestHasMasterField;}
     /**
      * For debugging.
      */
@@ -183,6 +187,7 @@ private:
     CopyNodePtr headNode;
     epics::pvData::PVStructurePtr cacheInitStructure;
     epics::pvData::BitSetPtr ignorechangeBitSet;
+    bool requestHasMasterField;
 
     void traverseMaster(
         CopyNodePtr const &node,