diff --git a/moto/s3/responses.py b/moto/s3/responses.py
index 43e27a815..dbc6bf28f 100644
--- a/moto/s3/responses.py
+++ b/moto/s3/responses.py
@@ -484,7 +484,7 @@ class ResponseObject(_TemplateEnvironmentMixin):
         elif method == 'PUT':
             return self._key_response_put(request, body, bucket_name, query, key_name, headers)
         elif method == 'HEAD':
-            return self._key_response_head(bucket_name, query, key_name, headers)
+            return self._key_response_head(bucket_name, query, key_name, headers=request.headers)
         elif method == 'DELETE':
             return self._key_response_delete(bucket_name, query, key_name, headers)
         elif method == 'POST':
@@ -597,7 +597,7 @@ class ResponseObject(_TemplateEnvironmentMixin):
         response_headers = {}
         version_id = query.get('versionId', [None])[0]
 
-        if_modified_since = headers.get('if-modified-since', None)
+        if_modified_since = headers.get('If-Modified-Since', None)
         if if_modified_since:
             if_modified_since = str_to_rfc_1123_datetime(if_modified_since)
 
diff --git a/tests/test_s3/test_s3.py b/tests/test_s3/test_s3.py
index 6af653f9e..cd1c2e43e 100644
--- a/tests/test_s3/test_s3.py
+++ b/tests/test_s3/test_s3.py
@@ -1277,18 +1277,17 @@ def test_boto3_head_object_if_modified_since():
 
     key = 'hello.txt'
 
-    with freeze_time(datetime.datetime.now() - datetime.timedelta(hours=3)):
-        s3.put_object(
-            Bucket=bucket_name,
-            Key=key,
-            Body='test'
-        )
+    s3.put_object(
+        Bucket=bucket_name,
+        Key=key,
+        Body='test'
+    )
 
     with assert_raises(botocore.exceptions.ClientError) as err:
         s3.head_object(
             Bucket=bucket_name,
             Key=key,
-            IfModifiedSince=datetime.datetime.now() - datetime.timedelta(hours=2)
+            IfModifiedSince=datetime.datetime.utcnow() + datetime.timedelta(hours=1)
         )
     e = err.exception
     e.response['Error'].should.equal({'Code': '304', 'Message': 'Not Modified'})