diff --git a/tests/unittests/tests-phydat/Makefile b/tests/unittests/tests-phydat/Makefile
new file mode 100644
index 000000000000..48422e909a47
--- /dev/null
+++ b/tests/unittests/tests-phydat/Makefile
@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base
diff --git a/tests/unittests/tests-phydat/Makefile.include b/tests/unittests/tests-phydat/Makefile.include
new file mode 100644
index 000000000000..7583f4db7aaa
--- /dev/null
+++ b/tests/unittests/tests-phydat/Makefile.include
@@ -0,0 +1 @@
+USEMODULE += phydat
diff --git a/tests/unittests/tests-phydat/tests-phydat.c b/tests/unittests/tests-phydat/tests-phydat.c
new file mode 100644
index 000000000000..af7e7b99a171
--- /dev/null
+++ b/tests/unittests/tests-phydat/tests-phydat.c
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2018 Eistec AB
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+#include "embUnit.h"
+#include "tests-phydat.h"
+
+#include "phydat.h"
+
+#define ENABLE_DEBUG (0)
+#include "debug.h"
+
+static void test_phydat_fit(void)
+{
+    /* verify that these big numbers are scaled to fit in phydat_t::val which is int16_t */
+    long val0 =   100445;
+    long val1 =  2000954;
+    long val2 = 30000455;
+    long val4 =  1234567;
+    phydat_t dat;
+    dat.scale = -6;
+    dat.unit = UNIT_V;
+    uint8_t res = phydat_fit(&dat, val0, 0, 0);
+    /* Check that the result was rescaled to 10044e-5 */
+    /* The scaled number is rounded toward zero */
+    TEST_ASSERT_EQUAL_INT(1, res);
+    TEST_ASSERT_EQUAL_INT(UNIT_V, dat.unit);
+    TEST_ASSERT_EQUAL_INT(-5, dat.scale);
+    TEST_ASSERT_EQUAL_INT( 10044, dat.val[0]);
+    /* Fit the next value in the phydat vector */
+    res = phydat_fit(&dat, val1, 1, res);
+    TEST_ASSERT_EQUAL_INT(2, res);
+    TEST_ASSERT_EQUAL_INT(UNIT_V, dat.unit);
+    TEST_ASSERT_EQUAL_INT(-4, dat.scale);
+    TEST_ASSERT_EQUAL_INT(  1004, dat.val[0]);
+    TEST_ASSERT_EQUAL_INT( 20009, dat.val[1]);
+    /* Fit the third value in the phydat vector */
+    res = phydat_fit(&dat, val2, 2, res);
+    TEST_ASSERT_EQUAL_INT(3, res);
+    TEST_ASSERT_EQUAL_INT(UNIT_V, dat.unit);
+    TEST_ASSERT_EQUAL_INT(-3, dat.scale);
+    TEST_ASSERT_EQUAL_INT(   100, dat.val[0]);
+    TEST_ASSERT_EQUAL_INT(  2000, dat.val[1]);
+    TEST_ASSERT_EQUAL_INT( 30000, dat.val[2]);
+    /* Overwrite the second value in the phydat vector */
+    res = phydat_fit(&dat, val4, 1, res);
+    TEST_ASSERT_EQUAL_INT(3, res);
+    TEST_ASSERT_EQUAL_INT(UNIT_V, dat.unit);
+    TEST_ASSERT_EQUAL_INT(-3, dat.scale);
+    TEST_ASSERT_EQUAL_INT(   100, dat.val[0]);
+    TEST_ASSERT_EQUAL_INT(  1234, dat.val[1]);
+    TEST_ASSERT_EQUAL_INT( 30000, dat.val[2]);
+}
+
+Test *tests_phydat_tests(void)
+{
+    EMB_UNIT_TESTFIXTURES(fixtures) {
+        new_TestFixture(test_phydat_fit),
+    };
+
+    EMB_UNIT_TESTCALLER(phydat_tests, NULL, NULL, fixtures);
+
+    return (Test *)&phydat_tests;
+}
+
+void tests_phydat(void)
+{
+    TESTS_RUN(tests_phydat_tests());
+}
diff --git a/tests/unittests/tests-phydat/tests-phydat.h b/tests/unittests/tests-phydat/tests-phydat.h
new file mode 100644
index 000000000000..1697ecba831d
--- /dev/null
+++ b/tests/unittests/tests-phydat/tests-phydat.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2018 Eistec AB
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @addtogroup  unittests
+ * @{
+ *
+ * @file
+ * @brief       Unittests for the phydat module
+ *
+ * @author      Joakim Nohlgård <joakim.nohlgard@eistec.se>
+ */
+#ifndef TESTS_PHYDAT_H
+#define TESTS_PHYDAT_H
+#include "embUnit/embUnit.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+*  @brief   The entry point of this test suite.
+*/
+void tests_phydat(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* TESTS_PHYDAT_H */
+/** @} */