diff --git a/src/logging.c b/src/logging.c
index 35746e9..b96e64a 100644
--- a/src/logging.c
+++ b/src/logging.c
@@ -190,6 +190,7 @@
 		target->categories[i].enabled = 0;
 
 	category_token = strtok(mask, ":");
+	OSMO_ASSERT(category_token);
 	do {
 		for (i = 0; i < osmo_log_info->num_cat; ++i) {
 			size_t length, cat_length;