diff --git a/tests/posix_sleep/Makefile b/tests/posix_sleep/Makefile
index 32fefc14e52d4a81d848dc15331ce2e9bf2bf325..035d06fff2f2168a55d22ac54243fdfa2ed20458 100644
--- a/tests/posix_sleep/Makefile
+++ b/tests/posix_sleep/Makefile
@@ -1,12 +1,6 @@
 APPLICATION = posix_sleep
 include ../Makefile.tests_common
 
-BOARD_BLACKLIST := arduino-mega2560
-# arduino-mega2560: warning: iteration 2u invokes undefined behavior
-# [-Waggressive-loop-optimizations]
-
 USEMODULE += posix
 
-DISABLE_MODULE += auto_init
-
 include $(RIOTBASE)/Makefile.include
diff --git a/tests/posix_sleep/main.c b/tests/posix_sleep/main.c
index babb406cab7b389d8df1091d361d7ce0f0ca39ba..02c153766cbc44543c898806b1d7bce2d7d42c34 100644
--- a/tests/posix_sleep/main.c
+++ b/tests/posix_sleep/main.c
@@ -25,7 +25,7 @@ int main(void)
 {
     puts("usleep 1 x 1000*1000");
     for (int i = 0; i < 10; i++) {
-        useconds_t us = i*1000*1000;
+        useconds_t us = i*1000u*1000u;
         printf("calling usleep(%u)\n", (unsigned int) us);
         usleep(us);
         puts("wake up");
diff --git a/tests/pthread/Makefile b/tests/pthread/Makefile
index f94b94daf7a3b70ab278b66f70b71b96958b81e4..ba9e5aed5660d716f6bf6d6a1926ede8cf320a34 100644
--- a/tests/pthread/Makefile
+++ b/tests/pthread/Makefile
@@ -7,6 +7,4 @@ BOARD_BLACKLIST := arduino-mega2560
 USEMODULE += posix
 USEMODULE += pthread
 
-DISABLE_MODULE += auto_init
-
 include $(RIOTBASE)/Makefile.include
diff --git a/tests/pthread_cooperation/Makefile b/tests/pthread_cooperation/Makefile
index 996c3fa30e6f1b54df69574c9c824baf33f0e8e5..e9f15d5469d0d7c36854ba4ef71657dddb1d2c62 100644
--- a/tests/pthread_cooperation/Makefile
+++ b/tests/pthread_cooperation/Makefile
@@ -7,6 +7,4 @@ BOARD_BLACKLIST := arduino-mega2560
 USEMODULE += posix
 USEMODULE += pthread
 
-DISABLE_MODULE += auto_init
-
 include $(RIOTBASE)/Makefile.include
diff --git a/tests/pthread_tls/Makefile b/tests/pthread_tls/Makefile
index e4b10419fdf8cc1593c47d71ca35b62730c2a872..d30f9c0368c5d97947f519c200bf9db47c6dc0f6 100644
--- a/tests/pthread_tls/Makefile
+++ b/tests/pthread_tls/Makefile
@@ -7,6 +7,4 @@ BOARD_BLACKLIST := arduino-mega2560
 USEMODULE += posix
 USEMODULE += pthread
 
-DISABLE_MODULE += auto_init
-
 include $(RIOTBASE)/Makefile.include