diff --git a/app/controllers/assays_controller.rb b/app/controllers/assays_controller.rb
index 796642c82d..dab907ae86 100644
--- a/app/controllers/assays_controller.rb
+++ b/app/controllers/assays_controller.rb
@@ -114,6 +114,7 @@ def create
 
   def delete_linked_sample_types
     return unless is_single_page_assay?
+    return if @assay.sample_type.nil?
 
     @assay.sample_type.destroy
   end
diff --git a/app/controllers/studies_controller.rb b/app/controllers/studies_controller.rb
index 4386e966b9..a657e6ce9e 100644
--- a/app/controllers/studies_controller.rb
+++ b/app/controllers/studies_controller.rb
@@ -90,6 +90,7 @@ def update
 
   def delete_linked_sample_types
     return unless is_single_page_study?
+    return if @study.sample_types.empty?
 
     # The study sample types must be destroyed in reversed order
     # otherwise the first sample type won't be removed becaused it is linked from the second