diff --git a/CHANGES/13580.bugfix.rst b/CHANGES/13580.bugfix.rst
new file mode 100644
index 00000000000..62406696f14
--- /dev/null
+++ b/CHANGES/13580.bugfix.rst
@@ -0,0 +1 @@
+Fixed ``BaseRequest.http_range`` not accepting case-insensitive range units -- by :user:`Manny7717`.
diff --git a/CHANGES/13581.bugfix.rst b/CHANGES/13581.bugfix.rst
new file mode 120000
index 00000000000..402ff87b6a1
--- /dev/null
+++ b/CHANGES/13581.bugfix.rst
@@ -0,0 +1 @@
+13580.bugfix.rst
\ No newline at end of file
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 3748922ee71..5e8f0e74486 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -258,6 +258,7 @@ Lukasz Marcin Dobrzanski
 Lukshya Supyal
 Lénárd Szolnoki
 Makc Belousow
+Manny7717
 Manuel Miranda
 Marat Sharafutdinov
 Marc Mueller
diff --git a/aiohttp/web_request.py b/aiohttp/web_request.py
index 5f426d743c7..5938c718a60 100644
--- a/aiohttp/web_request.py
+++ b/aiohttp/web_request.py
@@ -641,7 +641,8 @@ def http_range(self) -> "slice[int, int, int]":
         if rng is not None:
             try:
                 pattern = r"^bytes=(\d*)-(\d*)$"
-                start, end = re.findall(pattern, rng, re.ASCII)[0]
+                # https://www.rfc-editor.org/info/rfc9110/#section-14.1-4
+                start, end = re.findall(pattern, rng, re.ASCII | re.IGNORECASE)[0]
             except IndexError:  # pattern was not found in header
                 raise ValueError("range not in acceptable format")
 
diff --git a/tests/test_web_request.py b/tests/test_web_request.py
index d1b6f553a99..760be892f4a 100644
--- a/tests/test_web_request.py
+++ b/tests/test_web_request.py
@@ -316,6 +316,15 @@ def test_range_non_ascii() -> None:
         req.http_range
 
 
+def test_range_to_slice_uppercase_unit() -> None:
+    # https://www.rfc-editor.org/info/rfc9110/#section-14.1-4
+    req = make_mocked_request(
+        "GET", "/", headers=CIMultiDict([("RANGE", "Bytes=0-499")])
+    )
+    assert isinstance(req.http_range, slice)
+    assert req.http_range.start == 0 and req.http_range.stop == 500
+
+
 def test_non_keepalive_on_http10() -> None:
     req = make_mocked_request("GET", "/", version=HttpVersion(1, 0))
     assert not req.keep_alive