From 80edb84a04b7bef2273010e728aeff63a15c4d82 Mon Sep 17 00:00:00 2001
From: Bill Cleveland <120688282+BillCleveland-USRA@users.noreply.github.com>
Date: Fri, 12 May 2023 09:39:04 -0500
Subject: [PATCH] Fixed issue 14808: Added condition type(recformat) ==
 _FormatP to mitigate the issue cause by _FormatQ is a subclass of _FormatP.
 Added regress test for Issue 14808. Added "what's new" file for pull 14810.

---
 astropy/io/fits/fitsrec.py            |  2 +-
 astropy/io/fits/tests/test_table.py   | 23 +++++++++++++++++++++++
 docs/changes/io.fits/14810.bugfix.rst |  2 ++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 docs/changes/io.fits/14810.bugfix.rst

diff --git a/astropy/io/fits/fitsrec.py b/astropy/io/fits/fitsrec.py
index a9addc8b811..4552cc8322c 100644
--- a/astropy/io/fits/fitsrec.py
+++ b/astropy/io/fits/fitsrec.py
@@ -1130,7 +1130,7 @@ def _scale_back(self, update_heap_pointers=True):
                 # Even if this VLA has not been read or updated, we need to
                 # include the size of its constituent arrays in the heap size
                 # total
-                if heapsize >= 2**31:
+                if type(recformat) == _FormatP and heapsize >= 2**31:
                     raise ValueError(
                         "The heapsize limit for 'P' format has been reached. "
                         "Please consider using the 'Q' format for your file."
diff --git a/astropy/io/fits/tests/test_table.py b/astropy/io/fits/tests/test_table.py
index 31512839510..66a1e35e35e 100644
--- a/astropy/io/fits/tests/test_table.py
+++ b/astropy/io/fits/tests/test_table.py
@@ -3230,6 +3230,29 @@ def test_heapsize_P_limit(self):
         ):
             t.writeto(self.temp("matrix.fits"))
 
+    @pytest.mark.skipif(sys.maxsize < 2**32, reason="requires 64-bit system")
+    @pytest.mark.skipif(sys.platform == "win32", reason="Cannot test on Windows")
+    @pytest.mark.hugemem
+    def test_heapsize_Q_limit(self):
+        """
+        Regression test for https://github.com/astropy/astropy/issues/14808
+
+        Check if the error is no longer raised when the heap size is bigger than what can be
+        indexed with a 32 bit signed int.
+        """
+
+        # a matrix with variable length array elements is created
+        nelem = 2**28
+        matrix = np.zeros(1, dtype=np.object_)
+        matrix[0] = np.arange(0.0, float(nelem + 1))
+
+        col = fits.Column(name="MATRIX", format=f"QD({nelem})", unit="", array=matrix)
+
+        t = fits.BinTableHDU.from_columns([col])
+        t.name = "MATRIX"
+
+        t.writeto(self.temp("matrix.fits"))
+
     def test_empty_vla_raw_data(self):
         """
         Regression test for https://github.com/astropy/astropy/issues/12881
diff --git a/docs/changes/io.fits/14810.bugfix.rst b/docs/changes/io.fits/14810.bugfix.rst
new file mode 100644
index 00000000000..c2736bf0530
--- /dev/null
+++ b/docs/changes/io.fits/14810.bugfix.rst
@@ -0,0 +1,2 @@
+Fixes an issue where FITS_rec was incorrectly raising a ValueError exception when the heapsize was greater than 2**31
+when the Column type was 'Q' instead of 'P'.