diff --git a/CHANGELOG-EE b/CHANGELOG-EE
index d5fabbb0cb9877b3d256c0760bfbdac59d089a9b..fa48f15ae86a6c3b3ed931437ad7864dc1164337 100644
--- a/CHANGELOG-EE
+++ b/CHANGELOG-EE
@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.10.0 (unreleased)
   - Rename Git Hooks to Push Rules
+  - Fix merge request 500 when first commit does not have a parent. !525
 
 v 8.9.4
   - Improve how File Lock feature works with nested items. !497
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index c56844cd73a00aaec7426f99ed3e98a241062cc3..81d6a151fc5d3e848a406166f97bd395bd79b48a 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -629,7 +629,8 @@ def in_locked_state
   end
 
   def source_sha_parent
-    source_project.repository.commit(first_commit.sha).parents.first.sha
+    parents = source_project.repository.commit(first_commit.sha).parents
+    parents.first.sha unless parents.empty?
   end
 
   def ff_merge_possible?
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index 1ff436fb67c22348179bf75267737e73cf1d7a58..8ff5fdd199cc0337cee5acc1415eccb7bc0992c7 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -331,9 +331,21 @@
     end
   end
 
-  describe "#source_sha_parent" do
-    it "returns the sha of the parent commit of the first commit in the MR" do
-      expect(subject.source_sha_parent).to eq("ae73cb07c9eeaf35924a10f713b364d32b2dd34f")
+  describe '#source_sha_parent' do
+    it 'returns the sha of the parent commit of the first commit in the MR' do
+      expect(subject.source_sha_parent).to eq('ae73cb07c9eeaf35924a10f713b364d32b2dd34f')
+    end
+
+    it 'returns nil when the first commit in the MR has no parents' do
+      allow_any_instance_of(Commit).to receive(:parents).and_return([])
+
+      expect(subject.source_sha_parent).to be_nil
+    end
+
+    it 'does not raise an error when the first commit in the MR has no parents' do
+      allow_any_instance_of(Commit).to receive(:parents).and_return([])
+
+      expect { subject.source_sha_parent }.not_to raise_error
     end
   end