diff --git a/ciao_contrib/_tools/merging.py b/ciao_contrib/_tools/merging.py
index 9aebc982..d72ab748 100644
--- a/ciao_contrib/_tools/merging.py
+++ b/ciao_contrib/_tools/merging.py
@@ -49,6 +49,7 @@
 import ciao_contrib._tools.utils as utils
 
 from ciao_contrib._tools.headers import HeaderMerge
+from ciao_contrib.stacklib import TemporaryStack
 
 __all__ = (
     "match_obsid",
@@ -2869,15 +2870,16 @@ def merge_psfmaps(mergetype, psfmap, psfmap_files, expmap_files,
     outfile = "{}[PSFMAP]".format(psfmap)
     if mergetype in dmfilttypes:
 
-        run.punlearn("dmimgfilt")
-        args = ["infile={}".format(','.join(psfmap_files)),
-                "outfile={}".format(outfile),
-                "function={}".format(mergetype),
-                "mask=point(0,0)",
-                "lookupTab={}".format(lookupTable),
-                "clobber={}".format(clstr),
-                "verbose={}".format(verbose)]
-        run.run("dmimgfilt", args)
+        with TemporaryStack(psfmap_files, dir=tmpdir) as tmp_stk:
+            run.punlearn("dmimgfilt")
+            args = ["infile=@{}".format(tmp_stk.name),
+                    "outfile={}".format(outfile),
+                    "function={}".format(mergetype),
+                    "mask=point(0,0)",
+                    "lookupTab={}".format(lookupTable),
+                    "clobber={}".format(clstr),
+                    "verbose={}".format(verbose)]
+            run.run("dmimgfilt", args)
 
     elif mergetype == 'exptime':
 
diff --git a/ciao_contrib/stacklib.py b/ciao_contrib/stacklib.py
index f3e7297e..d9ffb777 100644
--- a/ciao_contrib/stacklib.py
+++ b/ciao_contrib/stacklib.py
@@ -1,13 +1,11 @@
-
-# Python35Support
-
 #
-#  Copyright (C) 2011, 2012, 2016, 2019  Smithsonian Astrophysical Observatory
+#  Copyright (C) 2011, 2012, 2016, 2019, 2025
+#  Smithsonian Astrophysical Observatory
 #
 #
 #  This program is free software; you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
-#  the Free Software Foundation; either version 2 of the License, or
+#  the Free Software Foundation; either version 3 of the License, or
 #  (at your option) any later version.
 #
 #  This program is distributed in the hope that it will be useful,
@@ -32,9 +30,10 @@
 
 import os
 import tempfile
+import contextlib
 
 
-__all__ = ("make_stackfile", )
+__all__ = ("make_stackfile", "TemporaryStack")
 
 
 def make_stackfile(infiles, dir="/tmp/", suffix='', delete=True):
@@ -68,4 +67,43 @@ def make_stackfile(infiles, dir="/tmp/", suffix='', delete=True):
     tfh.flush()
     return tfh
 
+
+class TemporaryStack(contextlib.AbstractContextManager):
+    '''
+    A context manager that will create a stack for a list of values.
+
+    If abspath=True, then it will save the values in the tempfile
+    with the full path name. If false then it will save the values
+    with a preceeding "!" so as not to append the path to the satck
+    file onto the values.
+    '''
+
+    def __init__(self, values, abspath=False, *args, **kwargs):
+        'Create temp stack and populate it with values'
+
+        # use ASCDS_WORK_PATH for tmpdir if not set
+        if 'dir' not in kwargs:
+            kwargs['dir'] = os.environ["ASCDS_WORK_PATH"]
+
+        # use ".lis" for suffix if not set
+        if 'suffix' not in kwargs:
+            kwargs['suffix'] = ".lis"
+
+        # Use 'w' so stack is always overwritten
+        self.tfh = tempfile.NamedTemporaryFile(mode='w', *args,**kwargs)
+
+        for val in values:
+            if abspath:
+                putstr = os.path.abspath(str(val))
+            else:
+                putstr = "!"+str(val)
+            self.tfh.write(putstr+"\n")
+
+        self.tfh.flush()
+        self.name = self.tfh.name
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        'Close the stack and delete file'
+        self.tfh.close()
+
 # End