diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py
index 93b10d26c84545..0176cdb1598153 100644
--- a/Lib/http/cookiejar.py
+++ b/Lib/http/cookiejar.py
@@ -53,7 +53,8 @@ def _debug(*args):
 HTTPONLY_ATTR = "HTTPOnly"
 HTTPONLY_PREFIX = "#HttpOnly_"
 DEFAULT_HTTP_PORT = str(http.client.HTTP_PORT)
-NETSCAPE_MAGIC_RGX = re.compile("#( Netscape)? HTTP Cookie File")
+NETSCAPE_MAGIC_RGX = re.compile("#( Netscape)? HTTP Cookie File",
+                                re.IGNORECASE)
 MISSING_FILENAME_TEXT = ("a filename was not supplied (nor was the CookieJar "
                          "instance initialised with one)")
 NETSCAPE_HEADER_TEXT =  """\
diff --git a/Misc/ACKS b/Misc/ACKS
index 49f3692dfd6b8f..cd7c7c03462f6f 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -709,6 +709,7 @@ Brian Harring
 Jonathan Hartley
 Travis B. Hartwell
 Henrik Harutyunyan
+Ashley Harvey
 Shane Harvey
 Larry Hastings
 Tim Hatch
diff --git a/Misc/NEWS.d/next/Library/2023-02-11-09-49-49.gh-issue-82039.caTE7O.rst b/Misc/NEWS.d/next/Library/2023-02-11-09-49-49.gh-issue-82039.caTE7O.rst
new file mode 100644
index 00000000000000..cb75ae83780eaf
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-02-11-09-49-49.gh-issue-82039.caTE7O.rst
@@ -0,0 +1,2 @@
+:meth:`http.cookiejar.FileCookieJar.load` now checks the first, format
+signature line in a case-insensitive manner. Patch by Ashley Harvey.