diff --git a/MDD/mdd.c b/MDD/mdd.c
index 93a6e277feabffc68a1ded5e8b09d8686693f58b..ec2bd06ccd10d1389b4f54152c4ee928425a5232 100644
--- a/MDD/mdd.c
+++ b/MDD/mdd.c
@@ -146,6 +146,7 @@ int main (int argc, char **argv)
 	if (!getparstring("file_B", &file_B)) file_B=NULL;
 	assert(file_B != NULL);
 	if (!getparstring("file_out", &file_out)) file_out=NULL;
+ 	assert(file_out != NULL);
 	if (!getparstring("file_dmat", &file_dmat)) file_dmat=NULL;
 	if (!getparint("one_file", &one_file)) one_file = 1;