diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d790e7850..5214d352d 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -9,7 +9,7 @@ repos:
         types: []
 
   - repo: https://github.com/PyCQA/isort
-    rev: 5.11.4
+    rev: 5.12.0
     hooks:
       - id: isort
 
@@ -26,7 +26,7 @@ repos:
       - id: yesqa
 
   - repo: https://github.com/Lucas-C/pre-commit-hooks
-    rev: v1.3.1
+    rev: v1.4.2
     hooks:
       - id: remove-tabs
         exclude: (Makefile$|\.bat$|\.cmake$|\.eps$|\.fits$|\.opt$)
@@ -39,7 +39,7 @@ repos:
           [flake8-2020, flake8-errmsg, flake8-implicit-str-concat]
 
   - repo: https://github.com/pre-commit/pygrep-hooks
-    rev: v1.9.0
+    rev: v1.10.0
     hooks:
       - id: python-check-blanket-noqa
       - id: rst-backticks
@@ -57,7 +57,7 @@ repos:
       - id: sphinx-lint
 
   - repo: https://github.com/tox-dev/tox-ini-fmt
-    rev: 0.5.2
+    rev: 0.6.1
     hooks:
       - id: tox-ini-fmt
 
diff --git a/CHANGES.rst b/CHANGES.rst
index 27dbd69bb..e35a55965 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,9 @@ Changelog (Pillow)
 9.5.0 (unreleased)
 ------------------
 
+- Handle more than one directory returned by pkg-config #6896
+  [sebastic, radarhere]
+
 - Do not retry past formats when loading all formats for the first time #6902
   [radarhere]
 
diff --git a/Tests/test_image.py b/Tests/test_image.py
index d261638f9..ad3346b5a 100644
--- a/Tests/test_image.py
+++ b/Tests/test_image.py
@@ -398,6 +398,17 @@ class TestImage:
         with pytest.raises(ValueError):
             source.alpha_composite(over, (0, 0), (0, -1))
 
+    def test_register_open_duplicates(self):
+        # Arrange
+        factory, accept = Image.OPEN["JPEG"]
+        id_length = len(Image.ID)
+
+        # Act
+        Image.register_open("JPEG", factory, accept)
+
+        # Assert
+        assert len(Image.ID) == id_length
+
     def test_registered_extensions_uninitialized(self):
         # Arrange
         Image._initialized = 0
diff --git a/Tests/test_qt_image_qapplication.py b/Tests/test_qt_image_qapplication.py
index 1fc816146..34609314c 100644
--- a/Tests/test_qt_image_qapplication.py
+++ b/Tests/test_qt_image_qapplication.py
@@ -6,7 +6,7 @@ with warnings.catch_warnings():
     warnings.simplefilter("ignore", category=DeprecationWarning)
     from PIL import ImageQt
 
-from .helper import assert_image_equal, assert_image_equal_tofile, hopper
+from .helper import assert_image_equal_tofile, assert_image_similar, hopper
 
 if ImageQt.qt_is_installed:
     from PIL.ImageQt import QPixmap
@@ -48,7 +48,7 @@ if ImageQt.qt_is_installed:
 def roundtrip(expected):
     result = ImageQt.fromqpixmap(ImageQt.toqpixmap(expected))
     # Qt saves all pixmaps as rgb
-    assert_image_equal(result, expected.convert("RGB"))
+    assert_image_similar(result, expected.convert("RGB"), 0.3)
 
 
 @pytest.mark.skipif(not ImageQt.qt_is_installed, reason="Qt bindings are not installed")
diff --git a/setup.py b/setup.py
index 243365681..4382c1a97 100755
--- a/setup.py
+++ b/setup.py
@@ -263,18 +263,18 @@ def _pkg_config(name):
             if not DEBUG:
                 command_libs.append("--silence-errors")
                 command_cflags.append("--silence-errors")
-            libs = (
+            libs = re.split(
+                r"(^|\s+)-L",
                 subprocess.check_output(command_libs, stderr=stderr)
                 .decode("utf8")
-                .strip()
-                .replace("-L", "")
-            )
-            cflags = (
-                subprocess.check_output(command_cflags)
+                .strip(),
+            )[::2][1:]
+            cflags = re.split(
+                r"(^|\s+)-I",
+                subprocess.check_output(command_cflags, stderr=stderr)
                 .decode("utf8")
-                .strip()
-                .replace("-I", "")
-            )
+                .strip(),
+            )[::2][1:]
             return libs, cflags
         except Exception:
             pass
@@ -473,8 +473,12 @@ class pil_build_ext(build_ext):
             else:
                 lib_root = include_root = root
 
-            _add_directory(library_dirs, lib_root)
-            _add_directory(include_dirs, include_root)
+            if lib_root is not None:
+                for lib_dir in lib_root:
+                    _add_directory(library_dirs, lib_dir)
+            if include_root is not None:
+                for include_dir in include_root:
+                    _add_directory(include_dirs, include_dir)
 
         # respect CFLAGS/CPPFLAGS/LDFLAGS
         for k in ("CFLAGS", "CPPFLAGS", "LDFLAGS"):
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 833473f78..ad0d25add 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -3406,7 +3406,8 @@ def register_open(id, factory, accept=None):
        reject images having another format.
     """
     id = id.upper()
-    ID.append(id)
+    if id not in ID:
+        ID.append(id)
     OPEN[id] = factory, accept