diff --git a/tests/unittests/main.c b/tests/unittests/main.c
index 8c6092b80b..99d8755ca4 100644
--- a/tests/unittests/main.c
+++ b/tests/unittests/main.c
@@ -31,6 +31,11 @@ int main(void)
     ztimer_init();
 #endif
 
+#if MODULE_ZTIMER64_USEC || MODULE_ZTIMER64_MSEC || MODULE_ZTIMER64_SEC
+    /* auto_init is disabled, but some modules depends on this module being initialized */
+    ztimer64_init();
+#endif
+
 #if IS_USED(MODULE_XTIMER) && !IS_USED(MODULE_ZTIMER_XTIMER_COMPAT)
     /* auto_init is disabled, but some modules depends on this module being initialized */
     xtimer_init();
diff --git a/tests/unittests/tests-fib/Makefile.include b/tests/unittests/tests-fib/Makefile.include
index 75e2535a55..de789fdcbe 100644
--- a/tests/unittests/tests-fib/Makefile.include
+++ b/tests/unittests/tests-fib/Makefile.include
@@ -1,3 +1,3 @@
 CFLAGS += -DFIB_DEVEL_HELPER -DUNIVERSAL_ADDRESS_SIZE=16 -DUNIVERSAL_ADDRESS_MAX_ENTRIES=40
 
-USEMODULE += fib
+USEMODULE += fib xtimer