diff --git a/app/models/tag.rb b/app/models/tag.rb
index 308240861e..3b1abc83a6 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -25,6 +25,8 @@ def untag!
 
   broadcast_with_warren
 
+  validates :oligo, length: { maximum: 30 }, allow_blank: true
+
   scope :sorted, -> { order(:map_id) }
 
   def name
diff --git a/app/sample_manifest_excel/sample_manifest_excel/tags/validator/formatting.rb b/app/sample_manifest_excel/sample_manifest_excel/tags/validator/formatting.rb
index 3dfbcbbd06..ca7ad7598a 100644
--- a/app/sample_manifest_excel/sample_manifest_excel/tags/validator/formatting.rb
+++ b/app/sample_manifest_excel/sample_manifest_excel/tags/validator/formatting.rb
@@ -14,6 +14,7 @@ def check_formatting
           return if value.blank?
 
           errors.add(:tag, 'must be a combination of A,C,G,T or N') unless value.match?(/\A[acgtnACGTN]+\z/)
+          errors.add(:tag, 'length must not exceed 30 characters') if value.length > 30
         end
       end
     end
diff --git a/spec/data/sample_manifest_excel/columns.yml b/spec/data/sample_manifest_excel/columns.yml
index 83329b9978..fedeeae1ab 100644
--- a/spec/data/sample_manifest_excel/columns.yml
+++ b/spec/data/sample_manifest_excel/columns.yml
@@ -31,7 +31,7 @@ i7:
     options:
       type: :textLength
       operator: :lessThanOrEqual
-      formula1: "255"
+      formula1: "30"
       allowBlank: false
       showInputMessage: true
       promptTitle: "i7"
@@ -45,7 +45,7 @@ i5:
     options:
       type: :textLength
       operator: :lessThanOrEqual
-      formula1: "255"
+      formula1: "30"
       allowBlank: false
       showInputMessage: true
       promptTitle: "i5"
diff --git a/spec/models/tag_group/form_object_spec.rb b/spec/models/tag_group/form_object_spec.rb
index 0f3671900a..a13d5fa058 100644
--- a/spec/models/tag_group/form_object_spec.rb
+++ b/spec/models/tag_group/form_object_spec.rb
@@ -100,6 +100,13 @@
         expect(tag_group_form_object.tag_group.tags.first.oligo).to eq('ACCTTGGA')
       end
     end
+
+    context 'when the oligos entered are longer than 30 charcters' do
+      it 'the model is invalid' do
+        tag_group_form_object.oligos_text = 'AAAAAAASACCCGGGTTTTTAAAAAATTTTTT'
+        expect(tag_group_form_object).not_to be_valid
+      end
+    end
   end
 
   context 'when no name is entered' do