diff --git a/ChangeLog b/ChangeLog
index 3fca953..c1e231f 100755
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,9 +1,10 @@
-2021-04-29
+2021-04-30
 
         * Version 2.0.0 released
         ========================
 
         Add ASCL shields to "About" page (#3630)
+        Use file function constructor in csspec (#3626)
         Add BINS method to csspec (#3606)
         Add hidden "fix_spat" parameter to cttsmap (#3562)
         Add optimizer setter to ctlikelihood base class
diff --git a/NEWS b/NEWS
index a9b46c6..cc92779 100755
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,6 @@
 New Features and Important Changes in ctools 2.0.0
 
-29 April 2021
+30 April 2021
 
 
 Introduction
@@ -287,6 +287,9 @@ None
 
 csspec - Generates Spectral Energy Distribution
 -----------------------------------------------
+The GModelSpectralFunc spectral model constructor is now used to convert any
+spectral model into a file function before spectral model fitting (#3626).
+
 Added BINS method that replaces the spectral model by a bin function that is
 implemented by the GammaLib class GModelSpectralBins. Using a bin function
 assures that spectral points are statistically independent (#3606).
diff --git a/README.md b/README.md
index cfa7aa6..89f17ce 100755
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 ctools information
 ==================
-* Version:             2.0.0.dev (29 April 2021)
+* Version:             2.0.0.dev (30 April 2021)
 * GammaLib dependency: 2.0.0.dev
 
 [![Build Status](https://cta-jenkins.irap.omp.eu/buildStatus/icon?job=ctools-integrate-os)](https://cta-jenkins.irap.omp.eu/job/ctools-integrate-os/)
@@ -127,8 +127,8 @@ the following:
      $ conda install ctools
 
 
-Unix Installation
-=================
+Linux Installation
+==================
 To build and install ctools, simply type the following:
 
      $ ./configure
@@ -161,14 +161,14 @@ ctools was correctly built.  Make sure that all tests were successful.
 
 Macintosh OS X Installation
 ============================
-ctools is known to work on various flavors of OS X.  To cope with
+ctools is known to work on various flavors of Mac OS.  To cope with
 different system versions and architectures, there are two Mac
 specific configure options:
 
      $ ./configure --enable-universalsdk[=PATH]
 
 creates a universal build of ctools.  The optional argument specifies
-which OSX SDK should be used to perform the build.  This defaults to
+which MacOS SDK should be used to perform the build.  This defaults to
 "/Developer/SDKs/MacOSX.10.4u.sdk".  Specify "/" when building on a 10.5
 system or higher, especially when building 64-bit code.
 
@@ -221,7 +221,8 @@ shared library (see "Known problems" below).
 
 Windows Installation
 ====================
-There have been no efforts so far to compile ctools under Windows.
+On Windows ctools needs to be installed into a virtual machine running
+a Linux distribution.
 
 
 Testing
diff --git a/cscripts/csspec.py b/cscripts/csspec.py
index 6b6c6e5..8f70550 100755
--- a/cscripts/csspec.py
+++ b/cscripts/csspec.py
@@ -368,23 +368,17 @@ class csspec(ctools.csobservation):
                                          ' Fixing "'+par.name()+'"')
                     par.fix()
 
-                # Kludge: convert spectral model into a file function
-                nbins       = self._ebounds.size()
-                num         = nbins * 20
-                energies    = gammalib.GEnergies(num, self._ebounds.emin(0),
-                                                      self._ebounds.emax(nbins-1))
-                _, filename = tempfile.mkstemp()
-                f = open(filename, 'w')
-                spectral    = model.spectral()
-                for energy in energies:
-                    value = spectral.eval(energy)
-                    f.write('%20.6f  %20e\n' % (energy.MeV(), value))
-                f.close()
-                spectral = gammalib.GModelSpectralFunc(filename, 1.0)
+                # Convert spectral model into a file function. The file
+                # function is logarithmically sampled in energy, with with
+                # 20 times the number of spectral bins
+                nbins    = self._ebounds.size()
+                num      = nbins * 50
+                energies = gammalib.GEnergies(num, self._ebounds.emin(0),
+                                                   self._ebounds.emax(nbins-1))
+                spectral = gammalib.GModelSpectralFunc(model.spectral(), energies)
                 model.spectral(spectral)
                 self._log_string(gammalib.EXPLICIT, ' Converting spectral model '
-                                 'into file function via temporary file "%s"' %
-                                 filename)
+                                 'into file function')
 
                 # Free the normalisation parameter which is assumed to be
                 # the first spectral parameter
diff --git a/doc/source/admin/release_history/2.0.rst b/doc/source/admin/release_history/2.0.rst
index c45b874..272f7d3 100644
--- a/doc/source/admin/release_history/2.0.rst
+++ b/doc/source/admin/release_history/2.0.rst
@@ -1,6 +1,6 @@
 .. _2.0:
 
-ctools 2.0 release (29 April 2021)
+ctools 2.0 release (30 April 2021)
 ==================================
 
 Overview
@@ -26,6 +26,8 @@ Improvements
 
 * [`3630 <https://cta-redmine.irap.omp.eu/issues/3630>`_] -
   Add ASCL shields to **About** page
+* [`3626 <https://cta-redmine.irap.omp.eu/issues/3626>`_] -
+  Use file function constructor in csspec
 * [`3606 <https://cta-redmine.irap.omp.eu/issues/3606>`_] -
   Add ``BINS`` method to :ref:`csspec`
 * [`3562 <https://cta-redmine.irap.omp.eu/issues/3562>`_] -