diff --git a/taglib/tagunion.cpp b/taglib/tagunion.cpp
index 6480dcba..d38520ae 100644
--- a/taglib/tagunion.cpp
+++ b/taglib/tagunion.cpp
@@ -118,6 +118,46 @@ namespace TagLib
     }
   }
 
+  template <size_t COUNT>
+  PropertyMap TagUnion<COUNT>::setProperties(const PropertyMap &properties)
+  {
+    //Record unassigned properties for each tag in the union
+    std::vector<PropertyMap> returnCandidates;
+    for (size_t i = 0; i < COUNT; ++i) {
+      if (d->tags[i])
+        returnCandidates.insert(returnCandidates.end(),
+          d->tags[i]->setProperties(properties));
+    }
+
+    if (!returnCandidates.empty()) {
+      //Only one tag present, return its unassigned properties
+      if (returnCandidates.size() == 1) {
+        return returnCandidates.front();
+      }
+
+      //Multiple tags in union:
+      //if a property has been assigned in any member tag
+      //remove it from ignored properties to return
+      PropertyMap propertiesCopy(properties);
+      for (std::vector<PropertyMap>::iterator i = returnCandidates.begin();
+        i != returnCandidates.end(); i++) {
+        for (PropertyMap::Iterator j = propertiesCopy.begin();
+          j != propertiesCopy.end();) {
+          if (!i->contains(j->first)) {
+            j = propertiesCopy.erase(j->first).begin();
+          }
+          else {
+            j++;
+          }
+        }
+      }
+    }
+
+    //No assignments made by union member tags.
+    //Return input (this should not happen)
+    return properties;
+  }
+
   template <size_t COUNT>
   String TagUnion<COUNT>::title() const
   {
diff --git a/taglib/tagunion.h b/taglib/tagunion.h
index 6c608210..dc36806b 100644
--- a/taglib/tagunion.h
+++ b/taglib/tagunion.h
@@ -58,8 +58,8 @@ namespace TagLib {
     void set(size_t index, Tag *tag);
 
     virtual PropertyMap properties() const;
-
     virtual void removeUnsupportedProperties(const StringList& properties);
+    virtual PropertyMap setProperties(const PropertyMap& properties);
 
     virtual String title() const;
     virtual String artist() const;