diff --git a/CHANGELOG.md b/CHANGELOG.md
index f54fa767..72f6983e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ All notable changes to this project will be documented in this file. The format
 ## Unreleased
 
 - Upgrade `pdfminer.six` from `20251230` to `20260107`. ([07a5ff6](https://github.com/jsvine/pdfplumber/commit/07a5ff6))
+- Ensure internally-opened file streams are closed during garbage collection, preventing `ResourceWarning` leaks when `PDF.close()` is not called. ([#1336](https://github.com/jsvine/pdfplumber/issues/1336))
 
 ## 0.11.9 — 2026-01-05
 
@@ -680,4 +681,3 @@ Whoops.
 
 ### Fixed
 - Fix find_gutters — should ignore `" "` chars
-
diff --git a/README.md b/README.md
index f6f1ce3e..c56a054c 100644
--- a/README.md
+++ b/README.md
@@ -574,6 +574,7 @@ Many thanks to the following users who've contributed ideas, features, and fixes
 - [Brandon Roberts](https://github.com/brandonrobertz)
 - [@ennamarie19](https://github.com/ennamarie19)
 - [Anton Ilin](https://github.com/bronislav)
+- [@ReinerBRO](https://github.com/ReinerBRO)
 
 ## Contributing
 
diff --git a/pdfplumber/pdf.py b/pdfplumber/pdf.py
index 9c42bc25..da43e331 100644
--- a/pdfplumber/pdf.py
+++ b/pdfplumber/pdf.py
@@ -1,6 +1,7 @@
 import itertools
 import logging
 import pathlib
+import weakref
 from io import BufferedReader, BytesIO
 from types import TracebackType
 from typing import Any, Dict, Generator, List, Literal, Optional, Tuple, Type, Union
@@ -22,6 +23,18 @@
 logger = logging.getLogger(__name__)
 
 
+def _close_stream_if_internal(
+    stream: Union[BufferedReader, BytesIO], stream_is_external: bool
+) -> None:
+    if stream_is_external:
+        return
+    try:
+        if not stream.closed:
+            stream.close()
+    except Exception:
+        pass
+
+
 class PDF(Container):
     cached_properties: List[str] = Container.cached_properties + ["_pages"]
 
@@ -39,6 +52,9 @@ def __init__(
     ):
         self.stream = stream
         self.stream_is_external = stream_is_external
+        self._stream_finalizer = weakref.finalize(
+            self, _close_stream_if_internal, stream, stream_is_external
+        )
         self.path = path
         self.pages_to_parse = pages
         self.laparams = None if laparams is None else LAParams(**laparams)
@@ -127,8 +143,7 @@ def close(self) -> None:
         for page in self.pages:
             page.close()
 
-        if not self.stream_is_external:
-            self.stream.close()
+        self._stream_finalizer()
 
     def __enter__(self) -> "PDF":
         return self
diff --git a/tests/test_resource_warning.py b/tests/test_resource_warning.py
new file mode 100644
index 00000000..4ae02fb8
--- /dev/null
+++ b/tests/test_resource_warning.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python
+import gc
+import logging
+import os
+import unittest
+import warnings
+
+import pdfplumber
+
+logging.disable(logging.ERROR)
+
+HERE = os.path.abspath(os.path.dirname(__file__))
+PDF_PATH = os.path.join(HERE, "pdfs/nics-background-checks-2015-11.pdf")
+PDF_NAME = os.path.basename(PDF_PATH)
+
+
+class Test(unittest.TestCase):
+    def test_internal_stream_no_resource_warning_after_gc(self):
+        with warnings.catch_warnings(record=True) as caught:
+            warnings.simplefilter("always", ResourceWarning)
+            pdf = pdfplumber.open(PDF_PATH)
+            _ = pdf.pages[0].chars[0]["text"]
+            del pdf
+            gc.collect()
+
+        leaked_file_warnings = [
+            w
+            for w in caught
+            if issubclass(w.category, ResourceWarning) and PDF_NAME in str(w.message)
+        ]
+        assert leaked_file_warnings == []
+
+    def test_external_stream_is_not_closed(self):
+        stream = open(PDF_PATH, "rb")
+        try:
+            pdf = pdfplumber.open(stream)
+            _ = pdf.pages[0].chars[0]["text"]
+            del pdf
+            gc.collect()
+            assert stream.closed is False
+        finally:
+            stream.close()