diff --git a/CHANGELOG.md b/CHANGELOG.md
index c9dc4d9..119bd5c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ All notable changes to this project will be documented in this file, in reverse
 
 ### Fixed
 - Cmake when not using ESP-IDF ([#11](https://github.com/tuupola/bm8563/pull/11))
+- BM8563_ALARM_SET confused mday and wday ([#14](https://github.com/tuupola/bm8563/issues/14), [#15](https://github.com/tuupola/bm8563/pull/15))
 
 ### Added
 - Support for reading and writing timers ([#8](https://github.com/tuupola/bm8563/pull/8)).
diff --git a/bm8563.c b/bm8563.c
index 27996c5..937beb9 100644
--- a/bm8563.c
+++ b/bm8563.c
@@ -199,7 +199,7 @@ bm8563_ioctl(const bm8563_t *bm, int16_t command, void *buffer)
             }
 
             /* 0..6 */
-            if (BM8563_ALARM_NONE == time->tm_mday) {
+            if (BM8563_ALARM_NONE == time->tm_wday) {
                 data[3] = BM8563_ALARM_DISABLE;
             } else {
                 data[3] = decimal2bcd(time->tm_wday);
diff --git a/tests/unit.c b/tests/unit.c
index fef41ef..2a26d72 100644
--- a/tests/unit.c
+++ b/tests/unit.c
@@ -431,6 +431,34 @@ should_read_and_write_control_status2(void)
     PASS();
 }
 
+TEST
+bug_14_should_set_alarm_weekday(void)
+{
+    struct tm datetime = {0};
+    struct tm datetime2 = {0};
+    bm8563_t bm;
+    bm.read = &mock_i2c_read;
+    bm.write = &mock_i2c_write;
+
+    /* Set weekday alarm enabled but mday alarm disabled. */
+    /* This tests that weekday uses tm_wday, not tm_mday. */
+    datetime.tm_min = BM8563_ALARM_NONE;
+    datetime.tm_hour = BM8563_ALARM_NONE;
+    datetime.tm_mday = BM8563_ALARM_NONE;
+    datetime.tm_wday = 3;
+
+    ASSERT(BM8563_OK == bm8563_init(&bm));
+    ASSERT(BM8563_OK == bm8563_ioctl(&bm, BM8563_ALARM_SET, &datetime));
+    ASSERT(BM8563_OK == bm8563_ioctl(&bm, BM8563_ALARM_READ, &datetime2));
+
+    /* Weekday should be 3, not disabled. */
+    ASSERT_EQ(datetime.tm_wday, datetime2.tm_wday);
+    /* mday should be disabled (ALARM_NONE). */
+    ASSERT_EQ(BM8563_ALARM_NONE, datetime2.tm_mday);
+
+    PASS();
+}
+
 GREATEST_MAIN_DEFS();
 
 int
@@ -459,5 +487,6 @@ main(int argc, char **argv)
     RUN_TEST(should_fail_write_time);
     RUN_TEST(should_read_and_write_control_status1);
     RUN_TEST(should_read_and_write_control_status2);
+    RUN_TEST(bug_14_should_set_alarm_weekday);
     GREATEST_MAIN_END();
 }