diff --git a/app/models/client.rb b/app/models/client.rb
index 83b5692cf..b8f31c86d 100644
--- a/app/models/client.rb
+++ b/app/models/client.rb
@@ -510,7 +510,7 @@ def re3data=(value)
   end
 
   def subjects=(value)
-    write_attribute(:subjects, Array.wrap(value))
+    write_attribute(:subjects, Array.wrap(value).uniq)
   end
 
   def opendoar=(value)
diff --git a/app/models/doi.rb b/app/models/doi.rb
index 1b6e3a3a2..c8c986cf6 100644
--- a/app/models/doi.rb
+++ b/app/models/doi.rb
@@ -1734,11 +1734,11 @@ def _fos_filter(subject_array)
   end
 
   def fields_of_science
-    _fos_filter(subjects)
+    _fos_filter(subjects).uniq
   end
 
   def fields_of_science_repository
-    _fos_filter(client&.subjects)
+    _fos_filter(client&.subjects).uniq
   end
 
   def fields_of_science_combined