diff --git a/gems/aws-sigv4/CHANGELOG.md b/gems/aws-sigv4/CHANGELOG.md
index bf1132754da..ea5e2c5eda3 100644
--- a/gems/aws-sigv4/CHANGELOG.md
+++ b/gems/aws-sigv4/CHANGELOG.md
@@ -1,6 +1,8 @@
 Unreleased Changes
 ------------------
 
+* Issue - Don't overwrite `host` header in sigv4 signer if given.
+
 1.2.0 (2020-06-17)
 ------------------
 
diff --git a/gems/aws-sigv4/lib/aws-sigv4/signer.rb b/gems/aws-sigv4/lib/aws-sigv4/signer.rb
index 78f01a6db55..799d1398adf 100644
--- a/gems/aws-sigv4/lib/aws-sigv4/signer.rb
+++ b/gems/aws-sigv4/lib/aws-sigv4/signer.rb
@@ -219,7 +219,7 @@ def sign_request(request)
         content_sha256 ||= sha256_hexdigest(request[:body] || '')
 
         sigv4_headers = {}
-        sigv4_headers['host'] = host(url)
+        sigv4_headers['host'] = headers['host'] || host(url)
         sigv4_headers['x-amz-date'] = datetime
         sigv4_headers['x-amz-security-token'] = creds.session_token if creds.session_token
         sigv4_headers['x-amz-content-sha256'] ||= content_sha256 if @apply_checksum_header
@@ -376,7 +376,7 @@ def presign_url(options)
         url = extract_url(options)
 
         headers = downcase_headers(options[:headers])
-        headers['host'] = host(url)
+        headers['host'] ||= host(url)
 
         datetime = headers['x-amz-date']
         datetime ||= (options[:time] || Time.now).utc.strftime("%Y%m%dT%H%M%SZ")
diff --git a/gems/aws-sigv4/spec/signer_spec.rb b/gems/aws-sigv4/spec/signer_spec.rb
index 96d5549fbcb..9d4640e699c 100644
--- a/gems/aws-sigv4/spec/signer_spec.rb
+++ b/gems/aws-sigv4/spec/signer_spec.rb
@@ -144,6 +144,16 @@ module Sigv4
           expect(signature.headers['host']).to eq('domain.com')
         end
 
+        context 'when a Host header is provided' do
+          it 'uses the provided Host header' do
+            signature = Signer.new(options).sign_request(
+              request.merge(headers: { 'host' => 'otherdomain.com' })
+            )
+
+            expect(signature.headers['host']).to eql('otherdomain.com')
+          end
+        end
+
         context 'when credentials are not set' do
           let(:creds) do
             Credentials.new(access_key_id: '', secret_access_key: '')