diff --git a/sys/include/timex.h b/sys/include/timex.h
index 66bd2f925e..fdfe37c794 100644
--- a/sys/include/timex.h
+++ b/sys/include/timex.h
@@ -55,6 +55,13 @@ int timex_isnormalized(timex_t *time);
  */
 uint64_t timex_uint64(const timex_t a);
 
+/**
+ * @brief Converts a uint64_t of microseconds to a timex_t
+ *
+ * @return a timex representation of an uint64 timestamp.
+ */
+timex_t timex_from_uint64(const uint64_t timestamp);
+
 /**
  * @brief Prints a timex_t
  */
diff --git a/sys/timex/timex.c b/sys/timex/timex.c
index b481c492f5..dce1edda41 100644
--- a/sys/timex/timex.c
+++ b/sys/timex/timex.c
@@ -14,6 +14,7 @@
  * @author Kaspar Schleiser <kaspar@schleiser.de>
  * @author Oliver Hahm <oliver.hahm@inria.fr>
  * @author Christian Mehlis <mehlis@inf.fu-berlin.de>
+ * @author Daniel Jentsch <d.jentsch@fu-berlin.de>
  *
  */
 
@@ -39,15 +40,11 @@ timex_t timex_add(const timex_t a, const timex_t b)
     result.seconds = a.seconds + b.seconds;
     result.microseconds = a.microseconds + b.microseconds;
 
-    if (result.microseconds < a.microseconds) {
+    if (result.microseconds > SEC_IN_USEC) {
+        result.microseconds -= SEC_IN_USEC;
         result.seconds++;
     }
 
-    /*    if (result.microseconds > SEC_IN_USEC) {
-            result.microseconds -= SEC_IN_USEC;
-            result.seconds++;
-        }
-    */
     return result;
 }
 
@@ -86,8 +83,15 @@ timex_t timex_sub(const timex_t a, const timex_t b)
 #endif
 
     timex_t result;
-    result.seconds = a.seconds - b.seconds;
-    result.microseconds = a.microseconds - b.microseconds;
+
+    if (a.microseconds >= b.microseconds) {
+        result.seconds = a.seconds - b.seconds;
+        result.microseconds = a.microseconds - b.microseconds;
+    }
+    else {
+        result.seconds = a.seconds - b.seconds - 1;
+        result.microseconds = a.microseconds + SEC_IN_USEC - b.microseconds;
+    }
 
     return result;
 }
@@ -122,6 +126,11 @@ uint64_t timex_uint64(const timex_t a)
     return (uint64_t) a.seconds * SEC_IN_USEC + a.microseconds;
 }
 
+timex_t timex_from_uint64(const uint64_t timestamp)
+{
+    return timex_set(timestamp / SEC_IN_USEC, timestamp % SEC_IN_USEC);
+}
+
 void timex_print(const timex_t t)
 {
     printf("Seconds: %" PRIu32 " - Microseconds: %" PRIu32 "\n", t.seconds, t.microseconds);
diff --git a/tests/unittests/tests-timex/Makefile b/tests/unittests/tests-timex/Makefile
new file mode 100644
index 0000000000..7eb455cc3c
--- /dev/null
+++ b/tests/unittests/tests-timex/Makefile
@@ -0,0 +1,3 @@
+MODULE = tests-timex
+
+include $(RIOTBASE)/Makefile.base
diff --git a/tests/unittests/tests-timex/Makefile.include b/tests/unittests/tests-timex/Makefile.include
new file mode 100644
index 0000000000..fde719b471
--- /dev/null
+++ b/tests/unittests/tests-timex/Makefile.include
@@ -0,0 +1,2 @@
+USEMODULE += timex
+
diff --git a/tests/unittests/tests-timex/tests-timex.c b/tests/unittests/tests-timex/tests-timex.c
new file mode 100644
index 0000000000..ca0b624387
--- /dev/null
+++ b/tests/unittests/tests-timex/tests-timex.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2014 Philipp Rosenkranz, Daniel Jentsch
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+#include "tests-timex.h"
+
+#include "timex.h"
+
+static void test_timex_set(void)
+{
+    timex_t time;
+    time = timex_set(1, 0);
+    TEST_ASSERT_EQUAL_INT(1, time.seconds);
+    TEST_ASSERT_EQUAL_INT(0, time.microseconds);
+}
+
+static void test_timex_add(void)
+{
+    timex_t time;
+    time = timex_add(timex_set(100, 100), timex_set(40, 10));
+    TEST_ASSERT_EQUAL_INT(0, timex_cmp(time, timex_set(140, 110)));
+    time = timex_add(timex_set(100, 700000), timex_set(40, 800000));
+    TEST_ASSERT_EQUAL_INT(0, timex_cmp(time, timex_set(141, 500000)));
+}
+
+static void test_timex_sub(void)
+{
+    timex_t time;
+    time = timex_sub(timex_set(100, 100), timex_set(40, 10));
+    TEST_ASSERT_EQUAL_INT(0, timex_cmp(time, timex_set(60, 90)));
+    time = timex_sub(timex_set(100, 100), timex_set(40, 200));
+    TEST_ASSERT_EQUAL_INT(0, timex_cmp(time, timex_set(59, 999900)));
+}
+
+static void test_timex_from_uint64(void)
+{
+    timex_t time;
+    time = timex_from_uint64(1001000);
+    TEST_ASSERT(time.seconds == 1);
+    TEST_ASSERT(time.microseconds == 1000);
+}
+
+Test *tests_timex_tests(void)
+{
+    EMB_UNIT_TESTFIXTURES(fixtures) {
+        new_TestFixture(test_timex_set),
+        new_TestFixture(test_timex_add),
+        new_TestFixture(test_timex_sub),
+        new_TestFixture(test_timex_from_uint64),
+    };
+
+    EMB_UNIT_TESTCALLER(timex_tests, NULL, NULL, fixtures);
+
+    return (Test *)&timex_tests;
+}
+
+void tests_timex(void)
+{
+    TESTS_RUN(tests_timex_tests());
+}
diff --git a/tests/unittests/tests-timex/tests-timex.h b/tests/unittests/tests-timex/tests-timex.h
new file mode 100644
index 0000000000..d65a33ca36
--- /dev/null
+++ b/tests/unittests/tests-timex/tests-timex.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2014 Philipp Rosenkranz, Daniel Jentsch
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @addtogroup  unittests
+ * @{
+ *
+ * @file        tests-timex.h
+ * @brief       Unittests for the ``timex`` module
+ *
+ * @author      Philipp Rosenkranz <philipp.rosenkranz@fu-berlin.de>
+ * @author      Daniel Jentsch <d.jentsch@fu-berlin.de>
+ */
+#ifndef __TESTS_TIMEX_H_
+#define __TESTS_TIMEX_H_
+
+#include "../unittests.h"
+
+/**
+ * @brief   The entry point of this test suite.
+ */
+void tests_timex(void);
+
+/**
+ * @brief   Generates tests for timex
+ *
+ * @return  embUnit tests if successful, NULL if not.
+ */
+Test *tests_timex_tests(void);
+
+#endif /* __TESTS_TIMEX_H_ */
+/** @} */