diff -ruN gwyddion-2.55.orig/configure.ac gwyddion-2.55/configure.ac
--- gwyddion-2.55.orig/configure.ac	2019-11-04 10:25:16.000000000 +0100
+++ gwyddion-2.55/configure.ac	2020-01-24 05:22:15.264763441 +0100
@@ -634,21 +634,25 @@
 #############################################################################
 # OpenEXR
 # Optional.  Used for HDR greyscale OpenEXR pixmap import/export.
-enable_exr=$have_cxx
-PKG_CHECK_MODULES(EXR, [OpenEXR],
+GWY_WITH([exr],,[build with OpenEXR support])
+if test "x$enable_exr" != "xno" && "x$have_cxx" != "xno"; then
+  PKG_CHECK_MODULES(EXR, [OpenEXR],
                   [AC_DEFINE(HAVE_EXR,1,
                             [Define if we have the OpenEXR package.])],
                   [enable_exr=no])
+fi
 AM_CONDITIONAL([HAVE_EXR],[test "x$enable_exr" != xno])
 
 #############################################################################
 # CFITSIO
 # Optional.  Used for FITS image import.
-enable_cfitsio=yes
-PKG_CHECK_MODULES(CFITSIO, [cfitsio],
+GWY_WITH([cfitsio],,[build with cfitsio support])
+if test "x$enable_cfitsio" != "xno"; then
+  PKG_CHECK_MODULES(CFITSIO, [cfitsio],
                   [AC_DEFINE(HAVE_CFITSIO,1,
                             [Define if we have the cfitsio package.])],
                   [enable_cfitsio=no])
+fi
 AM_CONDITIONAL([HAVE_CFITSIO],[test "x$enable_cfitsio" != xno])
 
 #############################################################################