diff --git a/CHANGES/13580.bugfix.rst b/CHANGES/13580.bugfix.rst
new file mode 100644
index 00000000000..4a903a93b5d
--- /dev/null
+++ b/CHANGES/13580.bugfix.rst
@@ -0,0 +1,5 @@
+Fixed :attr:`aiohttp.web.BaseRequest.http_range` rejecting ``Range`` headers whose
+range unit was not spelled in lowercase. Range unit names are case-insensitive per
+:rfc:`9110#section-14.1.1`, so ``Range: Bytes=0-3`` is valid and no longer causes
+:class:`aiohttp.web.FileResponse` to return ``416 Range Not Satisfiable``
+-- by :user:`LALITH0110`.
diff --git a/CHANGES/13584.bugfix.rst b/CHANGES/13584.bugfix.rst
new file mode 120000
index 00000000000..402ff87b6a1
--- /dev/null
+++ b/CHANGES/13584.bugfix.rst
@@ -0,0 +1 @@
+13580.bugfix.rst
\ No newline at end of file
diff --git a/aiohttp/web_request.py b/aiohttp/web_request.py
index 5f426d743c7..ff52aa39f04 100644
--- a/aiohttp/web_request.py
+++ b/aiohttp/web_request.py
@@ -640,8 +640,12 @@ def http_range(self) -> "slice[int, int, int]":
         start, end = None, None
         if rng is not None:
             try:
+                # Range unit names are case-insensitive (RFC 9110 sec. 14.1.1).
+                # re.ASCII is retained alongside re.IGNORECASE so that case
+                # folding stays ASCII-only: without it "byte\u017f=0-3" (LATIN
+                # SMALL LETTER LONG S) would also match.
                 pattern = r"^bytes=(\d*)-(\d*)$"
-                start, end = re.findall(pattern, rng, re.ASCII)[0]
+                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..76d5599f78e 100644
--- a/tests/test_web_request.py
+++ b/tests/test_web_request.py
@@ -316,6 +316,26 @@ def test_range_non_ascii() -> None:
         req.http_range
 
 
+@pytest.mark.parametrize("unit", ["bytes", "Bytes", "BYTES", "bYtEs"])
+def test_range_to_slice_unit_case_insensitive(unit: str) -> None:
+    # Range unit names are case-insensitive (RFC 9110 sec. 14.1.1).
+    req = make_mocked_request(
+        "GET", "/", headers=CIMultiDict([("RANGE", f"{unit}=0-499")])
+    )
+    assert isinstance(req.http_range, slice)
+    assert req.http_range.start == 0 and req.http_range.stop == 500
+
+
+def test_range_unit_non_ascii_case_fold() -> None:
+    # ſ = LATIN SMALL LETTER LONG S, which case-folds to "s" under Unicode
+    # rules. Matching is ASCII-only, so this is not a valid spelling of "bytes".
+    req = make_mocked_request(
+        "GET", "/", headers=CIMultiDict([("RANGE", "byteſ=0-499")])
+    )
+    with pytest.raises(ValueError, match="range not in acceptable format"):
+        req.http_range
+
+
 def test_non_keepalive_on_http10() -> None:
     req = make_mocked_request("GET", "/", version=HttpVersion(1, 0))
     assert not req.keep_alive