diff --git a/stix2/datastore/filesystem.py b/stix2/datastore/filesystem.py
index 2209116a..d6f83273 100644
--- a/stix2/datastore/filesystem.py
+++ b/stix2/datastore/filesystem.py
@@ -554,7 +554,7 @@ def __init__(self, stix_dir, allow_custom=False, bundlify=False):
     def stix_dir(self):
         return self._stix_dir
 
-    def _check_path_and_write(self, stix_obj, encoding='utf-8'):
+    def _check_path_and_write(self, stix_obj, encoding='utf-8', pretty=True):
         """Write the given STIX object to a file in the STIX file directory.
         """
         type_dir = os.path.join(self._stix_dir, stix_obj["type"])
@@ -585,9 +585,9 @@ def _check_path_and_write(self, stix_obj, encoding='utf-8'):
             raise DataSourceError("Attempted to overwrite file (!) at: {}".format(file_path))
 
         with io.open(file_path, mode='w', encoding=encoding) as f:
-            fp_serialize(stix_obj, f, pretty=True, encoding=encoding, ensure_ascii=False)
+            fp_serialize(stix_obj, f, pretty=pretty, encoding=encoding, ensure_ascii=False)
 
-    def add(self, stix_data=None, version=None):
+    def add(self, stix_data=None, version=None, pretty=True):
         """Add STIX objects to file directory.
 
         Args:
@@ -597,6 +597,7 @@ def add(self, stix_data=None, version=None):
             version (str): If present, it forces the parser to use the version
                 provided. Otherwise, the library will make the best effort based
                 on checking the "spec_version" property.
+            pretty (bool): If True, the resulting JSON will be "pretty printed"
 
         Note:
             ``stix_data`` can be a Bundle object, but each object in it will be
@@ -607,24 +608,24 @@ def add(self, stix_data=None, version=None):
         if isinstance(stix_data, (v20.Bundle, v21.Bundle)):
             # recursively add individual STIX objects
             for stix_obj in stix_data.get("objects", []):
-                self.add(stix_obj, version=version)
+                self.add(stix_obj, version=version, pretty=pretty)
 
         elif isinstance(stix_data, _STIXBase):
             # adding python STIX object
-            self._check_path_and_write(stix_data)
+            self._check_path_and_write(stix_data, pretty=pretty)
 
         elif isinstance(stix_data, (str, dict)):
             parsed_data = parse(stix_data, allow_custom=self.allow_custom, version=version)
             if isinstance(parsed_data, _STIXBase):
-                self.add(parsed_data, version=version)
+                self.add(parsed_data, version=version, pretty=pretty)
             else:
                 # custom unregistered object type
-                self._check_path_and_write(parsed_data)
+                self._check_path_and_write(parsed_data, pretty=pretty)
 
         elif isinstance(stix_data, list):
             # recursively add individual STIX objects
             for stix_obj in stix_data:
-                self.add(stix_obj)
+                self.add(stix_obj, version=version, pretty=pretty)
 
         else:
             raise TypeError(
diff --git a/stix2/test/v21/test_datastore_filesystem.py b/stix2/test/v21/test_datastore_filesystem.py
index 3eb20b5f..39b45578 100644
--- a/stix2/test/v21/test_datastore_filesystem.py
+++ b/stix2/test/v21/test_datastore_filesystem.py
@@ -151,6 +151,42 @@ def test_filesystem_source_bad_stix_file(fs_source, bad_stix_files):
     except STIXError as e:
         assert "Can't parse object with no 'type' property" in str(e)
 
+def test_filesystem_sink_add_pretty_true(fs_sink, fs_source):
+    """Test adding a STIX object with pretty=True."""
+    camp1 = stix2.v21.Campaign(
+        name="Hannibal",
+        objective="Targeting Italian and Spanish Diplomat internet accounts",
+        aliases=["War Elephant"],
+    )
+    fs_sink.add(camp1, pretty=True)
+    filepath = os.path.join(
+        FS_PATH, "campaign", camp1.id, _timestamp2filename(camp1.modified) + ".json",
+    )
+    assert os.path.exists(filepath)
+    with open(filepath, 'r', encoding='utf-8') as f:
+        content = f.read()
+        assert '\n' in content  # Check for pretty-printed output
+
+    os.remove(filepath)
+
+def test_filesystem_sink_add_pretty_false(fs_sink, fs_source):
+    """Test adding a STIX object with pretty=False."""
+    camp1 = stix2.v21.Campaign(
+        name="Hannibal",
+        objective="Targeting Italian and Spanish Diplomat internet accounts",
+        aliases=["War Elephant"],
+    )
+    fs_sink.add(camp1, pretty=False)
+    filepath = os.path.join(
+        FS_PATH, "campaign", camp1.id, _timestamp2filename(camp1.modified) + ".json",
+    )
+    assert os.path.exists(filepath)
+    with open(filepath, 'r', encoding='utf-8') as f:
+        content = f.read()
+        assert '\n' not in content  # Check for non-pretty-printed output
+
+    os.remove(filepath)
+
 
 def test_filesystem_source_get_object(fs_source):
     # get (latest) object