diff --git a/app/validators/sha_validator.rb b/app/validators/sha_validator.rb
index 085fca4d65d..77e7cfa4f6b 100644
--- a/app/validators/sha_validator.rb
+++ b/app/validators/sha_validator.rb
@@ -2,7 +2,7 @@
 
 class ShaValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
-    return if value.blank? || value.match(/\A\h{40}\z/)
+    return if value.blank? || Commit.valid_hash?(value)
 
     record.errors.add(attribute, 'is not a valid SHA')
   end
diff --git a/changelogs/unreleased/fj-58804-fix-bitbucket-import.yml b/changelogs/unreleased/fj-58804-fix-bitbucket-import.yml
new file mode 100644
index 00000000000..dc44c64a055
--- /dev/null
+++ b/changelogs/unreleased/fj-58804-fix-bitbucket-import.yml
@@ -0,0 +1,5 @@
+---
+title: Fix bug in BitBucket imports with SHA shorter than 40 chars
+merge_request: 26050
+author:
+type: fixed
diff --git a/spec/lib/gitlab/bitbucket_import/importer_spec.rb b/spec/lib/gitlab/bitbucket_import/importer_spec.rb
index c432cc223b9..e1a2bae5fe8 100644
--- a/spec/lib/gitlab/bitbucket_import/importer_spec.rb
+++ b/spec/lib/gitlab/bitbucket_import/importer_spec.rb
@@ -95,6 +95,9 @@ describe Gitlab::BitbucketImport::Importer do
   subject { described_class.new(project) }
 
   describe '#import_pull_requests' do
+    let(:source_branch_sha) { sample.commits.last }
+    let(:target_branch_sha) { sample.commits.first }
+
     before do
       allow(subject).to receive(:import_wiki)
       allow(subject).to receive(:import_issues)
@@ -102,9 +105,9 @@ describe Gitlab::BitbucketImport::Importer do
       pull_request = instance_double(
         Bitbucket::Representation::PullRequest,
         iid: 10,
-        source_branch_sha: sample.commits.last,
+        source_branch_sha: source_branch_sha,
         source_branch_name: Gitlab::Git::BRANCH_REF_PREFIX + sample.source_branch,
-        target_branch_sha: sample.commits.first,
+        target_branch_sha: target_branch_sha,
         target_branch_name: Gitlab::Git::BRANCH_REF_PREFIX + sample.target_branch,
         title: 'This is a title',
         description: 'This is a test pull request',
@@ -162,6 +165,19 @@ describe Gitlab::BitbucketImport::Importer do
       expect(reply_note).to be_a(DiffNote)
       expect(reply_note.note).to eq(@reply.note)
     end
+
+    context "when branches' sha is not found in the repository" do
+      let(:source_branch_sha) { 'a' * Commit::MIN_SHA_LENGTH }
+      let(:target_branch_sha) { 'b' * Commit::MIN_SHA_LENGTH }
+
+      it 'uses the pull request sha references' do
+        expect { subject.execute }.to change { MergeRequest.count }.by(1)
+
+        merge_request_diff = MergeRequest.first.merge_request_diff
+        expect(merge_request_diff.head_commit_sha).to eq source_branch_sha
+        expect(merge_request_diff.start_commit_sha).to eq target_branch_sha
+      end
+    end
   end
 
   context 'issues statuses' do
diff --git a/spec/validators/sha_validator_spec.rb b/spec/validators/sha_validator_spec.rb
index dc1539cf318..0a76570f65e 100644
--- a/spec/validators/sha_validator_spec.rb
+++ b/spec/validators/sha_validator_spec.rb
@@ -4,7 +4,7 @@ require 'spec_helper'
 
 describe ShaValidator do
   let(:validator) { described_class.new(attributes: [:base_commit_sha]) }
-  let(:merge_diff) { build(:merge_request_diff) }
+  let!(:merge_diff) { build(:merge_request_diff) }
 
   subject { validator.validate_each(merge_diff, :base_commit_sha, value) }
 
@@ -12,6 +12,8 @@ describe ShaValidator do
     let(:value) { nil }
 
     it 'does not add any error if value is empty' do
+      expect(Commit).not_to receive(:valid_hash?)
+
       subject
 
       expect(merge_diff.errors).to be_empty
@@ -21,7 +23,9 @@ describe ShaValidator do
   context 'with valid sha' do
     let(:value) { Digest::SHA1.hexdigest(SecureRandom.hex) }
 
-    it 'does not add any error if value is empty' do
+    it 'does not add any error' do
+      expect(Commit).to receive(:valid_hash?).and_call_original
+
       subject
 
       expect(merge_diff.errors).to be_empty
@@ -32,6 +36,7 @@ describe ShaValidator do
     let(:value) { 'foo' }
 
     it 'adds error to the record' do
+      expect(Commit).to receive(:valid_hash?).and_call_original
       expect(merge_diff.errors).to be_empty
 
       subject