diff --git a/CHANGELOG.md b/CHANGELOG.md
index fb089720..ea1271b4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -38,6 +38,9 @@ Status of the `main` branch. Changes prior to the next official version change w
     MCP session, since the MCP SDK v2 no longer provides session identifiers and client session usage
     was inconsistent anyway. Tools that need a session id (e.g. `activate_project`, the REPL tool) now
     take it as an explicit parameter, obtained from `initial_instructions`
+  - Performance: `Project.gather_source_files` transitively re-derived from the filesystem, for every path, 
+    whether that path was a file or a directory; related methods/functions now receive the information
+    as a parameter where it is already known (#2077)
 
 * CLI:
   - Fix: `project health-check` reported `Health check passed - All tools working correctly` and
diff --git a/src/serena/project.py b/src/serena/project.py
index 396a01cf..5f2570e5 100644
--- a/src/serena/project.py
+++ b/src/serena/project.py
@@ -212,7 +212,9 @@ class Project(ToStringMixin):
             )
         return self.__ignored_patterns
 
-    def _is_ignored_relative_path(self, relative_path: str | Path, ignore_non_source_files: bool = True) -> bool:
+    def _is_ignored_relative_path(
+        self, relative_path: str | Path, ignore_non_source_files: bool = True, is_file: bool | None = None
+    ) -> bool:
         """
         Determine whether a path should be ignored based on file type and ignore patterns.
         Returns False for non-existent paths since they cannot be matched by ignore patterns.
@@ -220,6 +222,7 @@ class Project(ToStringMixin):
         :param relative_path: Relative path to check
         :param ignore_non_source_files: whether files that are not source files (according to the file masks
             determined by the project's programming language) shall be ignored
+        :param is_file: whether the path exists and is a file, for callers that already know
 
         :return: whether the path should be ignored
         """
@@ -230,13 +233,16 @@ class Project(ToStringMixin):
             return False
 
         abs_path = os.path.join(self.project_root, relative_path)
-        if not os.path.exists(abs_path):
-            log.debug(f"Path {abs_path} does not exist, skipping ignore check")
-            return False
+        if is_file is None:
+            if not os.path.exists(abs_path):
+                log.debug(f"Path {abs_path} does not exist, skipping ignore check")
+                return False
 
         # check code file restriction (depending on backend)
         if ignore_non_source_files:
-            if os.path.isfile(abs_path):
+            if is_file is None:
+                is_file = os.path.isfile(abs_path)
+            if is_file:
                 # non-source files are ignored
                 if not self.language_backend.is_source_file(abs_path, self):
                     return True
@@ -248,15 +254,18 @@ class Project(ToStringMixin):
         if len(rel_path.parts) > 0 and ".git" in rel_path.parts:
             return True
 
-        return match_path(str(relative_path), self._ignore_spec, root_path=self.project_root)
+        is_dir = None if is_file is None else not is_file
+        return match_path(str(relative_path), self._ignore_spec, root_path=self.project_root, is_dir=is_dir)
 
-    def is_ignored_path(self, path: str | Path, ignore_non_source_files: bool = False) -> bool:
+    def is_ignored_path(self, path: str | Path, ignore_non_source_files: bool = False, is_file: bool | None = None) -> bool:
         """
         Checks whether the given path is ignored
 
         :param path: the path to check, can be absolute or relative
         :param ignore_non_source_files: whether to ignore files that are not source files
             (according to the file masks determined by the project's programming language)
+        :param is_file: whether the path exists and is a file, for callers that already know;
+            see :meth:`_is_ignored_relative_path`. `None` determines it from the filesystem.
         """
         path = Path(path)
         if path.is_absolute():
@@ -270,7 +279,7 @@ class Project(ToStringMixin):
         else:
             relative_path = path
 
-        return self._is_ignored_relative_path(str(relative_path), ignore_non_source_files=ignore_non_source_files)
+        return self._is_ignored_relative_path(str(relative_path), ignore_non_source_files=ignore_non_source_files, is_file=is_file)
 
     def get_is_ignored_path_fn(self, base_path: str, skip_ignored_paths: bool) -> Callable[[str], bool]:
         """
@@ -350,15 +359,17 @@ class Project(ToStringMixin):
         if os.path.isfile(start_path):
             return [relative_path]
         else:
+            # os.walk hands back directories and files separately, so `is_file` is already known here and
+            # does not have to be re-derived from the filesystem for every one of them.
             for root, dirs, files in os.walk(start_path, followlinks=True):
                 # prevent recursion into ignored directories
-                dirs[:] = [d for d in dirs if not self.is_ignored_path(os.path.join(root, d))]
+                dirs[:] = [d for d in dirs if not self.is_ignored_path(os.path.join(root, d), is_file=False)]
 
                 # collect non-ignored files
                 for file in files:
                     abs_file_path = os.path.join(root, file)
                     try:
-                        if not self.is_ignored_path(abs_file_path, ignore_non_source_files=True):
+                        if not self.is_ignored_path(abs_file_path, ignore_non_source_files=True, is_file=True):
                             try:
                                 rel_file_path = os.path.relpath(abs_file_path, start=self.project_root)
                             except Exception:
diff --git a/src/serena/util/file_system.py b/src/serena/util/file_system.py
index b08d483b..b78af51f 100644
--- a/src/serena/util/file_system.py
+++ b/src/serena/util/file_system.py
@@ -440,7 +440,7 @@ class GitignoreParser:
         self._load_gitignore_files()
 
 
-def match_path(relative_path: str, path_spec: PathSpec, root_path: str = "") -> bool:
+def match_path(relative_path: str, path_spec: PathSpec, root_path: str = "", is_dir: bool | None = None) -> bool:
     """
     Match a relative path against a given pathspec. Just pathspec.match_file() is not enough,
     we need to do some massaging to fix issues with pathspec matching.
@@ -448,6 +448,8 @@ def match_path(relative_path: str, path_spec: PathSpec, root_path: str = "") ->
     :param relative_path: relative path to match against the pathspec
     :param path_spec: the pathspec to match against
     :param root_path: the root path from which the relative path is derived
+    :param is_dir: whether the path is a directory, where the caller already knows; passing it avoids
+        an `os.path.isdir` call. `None` determines it from the filesystem.
     :return:
     """
     if str(relative_path) in {"", "."}:
@@ -465,7 +467,9 @@ def match_path(relative_path: str, path_spec: PathSpec, root_path: str = "") ->
 
     # pathspec can't handle the matching of directories if they don't end with a slash!
     # see https://github.com/cpburnz/python-pathspec/issues/89
-    abs_path = os.path.abspath(os.path.join(root_path, relative_path))
-    if os.path.isdir(abs_path) and not normalized_path.endswith("/"):
+    if is_dir is None:
+        abs_path = os.path.abspath(os.path.join(root_path, relative_path))
+        is_dir = os.path.isdir(abs_path)
+    if is_dir and not normalized_path.endswith("/"):
         normalized_path = normalized_path + "/"
     return path_spec.match_file(normalized_path)