diff --git a/app/services/merge_requests/merge_base_service.rb b/app/services/merge_requests/merge_base_service.rb
index 095bdca54726e06ba08acc5cac26d94580afc133..1ed396cee1e10a6799f3cc14dec37c913fa31b76 100644
--- a/app/services/merge_requests/merge_base_service.rb
+++ b/app/services/merge_requests/merge_base_service.rb
@@ -28,6 +28,17 @@ module MergeRequests
 
     private
 
+    def check_source
+      unless source
+        raise_error('No source for merge')
+      end
+    end
+
+    # Overridden in EE.
+    def check_size_limit
+      # No-op
+    end
+
     # Overridden in EE.
     def error_check!
       # No-op
diff --git a/app/services/merge_requests/merge_service.rb b/app/services/merge_requests/merge_service.rb
index d8a78001b79f03ec69a78e63cb7c8912ac8c8347..3e0f5aa181c54b1e293ff89805f06fffc9aed999 100644
--- a/app/services/merge_requests/merge_service.rb
+++ b/app/services/merge_requests/merge_service.rb
@@ -48,13 +48,13 @@ module MergeRequests
     def error_check!
       super
 
+      check_source
+
       error =
         if @merge_request.should_be_rebased?
           'Only fast-forward merge is allowed for your project. Please update your source branch'
         elsif !@merge_request.mergeable?
           'Merge request is not mergeable'
-        elsif !source
-          'No source for merge'
         end
 
       raise_error(error) if error
diff --git a/app/services/merge_requests/merge_to_ref_service.rb b/app/services/merge_requests/merge_to_ref_service.rb
index 0ea50a5dbf52e8016f6ae9e9b3c22ed0c3cbb2b0..37b5805ae7e4d3f234fd0aa1351049ad9eaef57c 100644
--- a/app/services/merge_requests/merge_to_ref_service.rb
+++ b/app/services/merge_requests/merge_to_ref_service.rb
@@ -16,7 +16,7 @@ module MergeRequests
     def execute(merge_request)
       @merge_request = merge_request
 
-      validate!
+      error_check!
 
       commit_id = commit
 
@@ -39,21 +39,9 @@ module MergeRequests
       merge_request.diff_head_sha
     end
 
-    def validate!
-      error_check!
-    end
-
+    override :error_check!
     def error_check!
-      super
-
-      error =
-        if !hooks_validation_pass?(merge_request)
-          hooks_validation_error(merge_request)
-        elsif source.blank?
-          'No source for merge'
-        end
-
-      raise_error(error) if error
+      check_source
     end
 
     ##
diff --git a/spec/services/merge_requests/merge_service_spec.rb b/spec/services/merge_requests/merge_service_spec.rb
index aa759ac9edc3f87666665c81cdfc8732cc051f8c..22578436c1852794db1aa8c07aa5d8180b327be7 100644
--- a/spec/services/merge_requests/merge_service_spec.rb
+++ b/spec/services/merge_requests/merge_service_spec.rb
@@ -214,6 +214,19 @@ describe MergeRequests::MergeService do
         allow(Rails.logger).to receive(:error)
       end
 
+      context 'when source is missing' do
+        it 'logs and saves error' do
+          allow(merge_request).to receive(:diff_head_sha) { nil }
+
+          error_message = 'No source for merge'
+
+          service.execute(merge_request)
+
+          expect(merge_request.merge_error).to eq(error_message)
+          expect(Rails.logger).to have_received(:error).with(a_string_matching(error_message))
+        end
+      end
+
       it 'logs and saves error if there is an exception' do
         error_message = 'error message'
 
diff --git a/spec/services/merge_requests/merge_to_ref_service_spec.rb b/spec/services/merge_requests/merge_to_ref_service_spec.rb
index 14012b4ea2d48587cf3ef2f7f3b5bd34a7ea2e54..758679edc4595c63159cd8523589aedcb199c369 100644
--- a/spec/services/merge_requests/merge_to_ref_service_spec.rb
+++ b/spec/services/merge_requests/merge_to_ref_service_spec.rb
@@ -191,6 +191,19 @@ describe MergeRequests::MergeToRefService do
       it { expect(todo).not_to be_done }
     end
 
+    context 'when source is missing' do
+      it 'returns error' do
+        allow(merge_request).to receive(:diff_head_sha) { nil }
+
+        error_message = 'No source for merge'
+
+        result = service.execute(merge_request)
+
+        expect(result[:status]).to eq(:error)
+        expect(result[:message]).to eq(error_message)
+      end
+    end
+
     context 'when target ref is passed as a parameter' do
       let(:params) { { commit_message: 'merge train', target_ref: target_ref } }