diff --git a/unittest/mgos_mock.c b/unittest/mgos_mock.c
index 063a142..dc15caf 100644
--- a/unittest/mgos_mock.c
+++ b/unittest/mgos_mock.c
@@ -7,6 +7,8 @@ int _mgos_timers = 0;
 
 int log_print_prefix(enum cs_log_level l, const char *func, const char *file) {
   char ll_str[6];
+  char fn_str[16];
+  char fu_str[41];
 
   switch (l) {
   case LL_ERROR:
@@ -30,9 +32,17 @@ int log_print_prefix(enum cs_log_level l, const char *func, const char *file) {
     break;
 
   default:   // LL_NONE
+    strncpy(ll_str, "?????", sizeof(ll_str));
     return 0;
   }
-  printf("%-5s %-15s %-40s| ", ll_str, file, func);
+
+  memset(fu_str, 0, sizeof(fu_str));
+  strncpy(fu_str, func, sizeof(fu_str)-1);
+
+  memset(fn_str, 0, sizeof(fn_str));
+  strncpy(fn_str, file, sizeof(fn_str)-1);
+
+  printf("%-5s %-15s %-40s| ", ll_str, fn_str, fu_str);
   return 1;
 }