Index: /issm/trunk-jpl/m4/issm_options.m4
===================================================================
--- /issm/trunk-jpl/m4/issm_options.m4	(revision 23341)
+++ /issm/trunk-jpl/m4/issm_options.m4	(revision 23342)
@@ -592,5 +592,5 @@
 	if test "x$HAVE_PYTHON" = "xyes"; then
 		AC_MSG_CHECKING([for python version])
-		dnl Query Python for its version number.  Getting [:3] seems to be the
+		dnl Query Python for its version number. Getting [:3] seems to be the
 		dnl best way to do this; it's what "site.py" does in the standard library.
 		PYTHON_VERSION=$($PYTHON_ROOT/bin/python -c "import sys; print sys.version[[:3]]")
@@ -644,4 +644,9 @@
 	  AS_HELP_STRING([--with-python-numpy-dir=DIR], [python-numpy root directory.]),
 	  [PYTHON_NUMPY_ROOT=$withval],[PYTHON_NUMPY_ROOT="no"])
+
+	dnl you can find numpy by typing
+	dnl >>> import numpy
+	dnl >>> numpy.__file__
+	dnl '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/numpy/__init__.pyc'
 
 	dnl Check whether numpy is enabled
@@ -2166,4 +2171,11 @@
 		AC_DEFINE([_MULTITHREADING_],[1],[with numthreads enabled])
 	fi
+	dnl check that it is an integer
+	if [[ "$NUMTHREADS_VALUE" -eq   "$NUMTHREADS_VALUE" 2> /dev/null ]] ; then
+	 dnl cool we have an integer
+	 :
+	else
+	 AC_MSG_ERROR([Number of threads provided ($NUMTHREADS_VALUE) is not an integer]);
+	fi
 	AC_DEFINE_UNQUOTED([_NUMTHREADS_],[$NUMTHREADS_VALUE],[number of threads])
 	AC_SUBST([MULTITHREADINGLIB])