diff --git a/configure.ac b/configure.ac
index 5a7465a..cc5a54d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -660,11 +660,13 @@ AM_CONDITIONAL([HAVE_CXX],[test "x$have_cxx" != xno])
 #############################################################################
 # OpenEXR 2.x+
 # Optional.  Used for HDR greyscale OpenEXR pixmap import/export.
-enable_exr=$have_cxx
-PKG_CHECK_MODULES(EXR, [OpenEXR >= 2.0],
+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 2.x+ package.])],
                   [enable_exr=no])
+fi
 AM_CONDITIONAL([HAVE_EXR],[test "x$enable_exr" != xno])
 
 #############################################################################
@@ -679,10 +681,13 @@ AM_CONDITIONAL([HAVE_HDF5],[test "x$enable_hdf5" != xno])
 #############################################################################
 # CFITSIO
 # Optional.  Used for FITS image import.
-PKG_CHECK_MODULES(CFITSIO, [cfitsio],
+GWY_WITH([cfitsio],,[build with cfitsio support])
+if test "x$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])
 
 #############################################################################