diff --git a/app/controllers/similar_topics_controller.rb b/app/controllers/similar_topics_controller.rb
index 31bfe272605..1f0a84d84f8 100644
--- a/app/controllers/similar_topics_controller.rb
+++ b/app/controllers/similar_topics_controller.rb
@@ -19,10 +19,11 @@ class SimilarTopicsController < ApplicationController
     params.require(:title)
     params.require(:raw)
     title, raw = params[:title], params[:raw]
-    [:title, :raw].each { |key| check_length_of(key, params[key]) }
+    invalid_length = [:title, :raw].any? { |key| check_invalid_length(key, params[key]) }
 
-    # Only suggest similar topics if the site has a minimum amount of topics present.
-    return render json: [] unless Topic.count_exceeds_minimum?
+    # Only suggest similar topics if the site has a minimum amount of topics present
+    # and params are long enough.
+    return render json: [] if invalid_length || !Topic.count_exceeds_minimum?
 
     topics = Topic.similar_to(title, raw, current_user).to_a
     topics.map! {|t| SimilarTopic.new(t) }
@@ -31,9 +32,9 @@ class SimilarTopicsController < ApplicationController
 
   protected
 
-    def check_length_of(key, attr)
+    def check_invalid_length(key, attr)
       str = (key == :raw) ? "body" : key.to_s
-      raise Discourse::InvalidParameters.new(key) if attr.length < SiteSetting.send("min_#{str}_similar_length")
+      attr.length < SiteSetting.send("min_#{str}_similar_length")
     end
 
 end
diff --git a/spec/controllers/similar_topics_controller_spec.rb b/spec/controllers/similar_topics_controller_spec.rb
index 5d5bc09ff43..fc6c3f9d47f 100644
--- a/spec/controllers/similar_topics_controller_spec.rb
+++ b/spec/controllers/similar_topics_controller_spec.rb
@@ -14,14 +14,20 @@ describe SimilarTopicsController do
       expect { xhr :get, :index, title: title }.to raise_error(ActionController::ParameterMissing)
     end
 
-    it "raises an error if the title length is below the minimum" do
+    it "returns no results if the title length is below the minimum" do
+      Topic.expects(:similar_to).never
       SiteSetting.stubs(:min_title_similar_length).returns(100)
-      expect { xhr :get, :index, title: title, raw: raw }.to raise_error(Discourse::InvalidParameters)
+      xhr :get, :index, title: title, raw: raw
+      json = ::JSON.parse(response.body)
+      expect(json["similar_topics"].size).to eq(0)
     end
 
-    it "raises an error if the body length is below the minimum" do
+    it "returns no results if the body length is below the minimum" do
+      Topic.expects(:similar_to).never
       SiteSetting.stubs(:min_body_similar_length).returns(100)
-      expect { xhr :get, :index, title: title, raw: raw }.to raise_error(Discourse::InvalidParameters)
+      xhr :get, :index, title: title, raw: raw
+      json = ::JSON.parse(response.body)
+      expect(json["similar_topics"].size).to eq(0)
     end
 
     describe "minimum_topics_similar" do