diff --git a/src/bam_filt.c b/src/bam_filt.c
index 3a2dc0a..08a6414 100644
--- a/src/bam_filt.c
+++ b/src/bam_filt.c
@@ -88,6 +88,10 @@ int parse_target_list(bam_hdr_t *header){
 	if(header->n_targets == 0) {
 		fprintf(stderr, "WARNING : no sequences in bam header : in : %s\n", __func__);
 	}
+
+ 	// strtok will cause a seg fault if you giv it a NULL at least for Unbuntu
+ 	if(bamfilt_global_opts.exclude_str == NULL) return 0;
+
 	char * pch = strtok (bamfilt_global_opts.exclude_str,",");
 	uint32_t nseq = 0;
 	while (pch != NULL)