diff --git a/tests/api-test-2.c b/tests/api-test-2.c
index 7acb82f6..d1f4b417 100644
--- a/tests/api-test-2.c
+++ b/tests/api-test-2.c
@@ -44,8 +44,6 @@ typedef int32_t key_serial_t;
 #include "luks1/luks.h"
 #include "libcryptsetup.h"
 
-#define DMDIR "/dev/mapper/"
-
 #define DEVICE_1_UUID "28632274-8c8a-493f-835b-da802e1c576b"
 #define DEVICE_EMPTY_name "crypt_zero"
 #define DEVICE_EMPTY DMDIR DEVICE_EMPTY_name
@@ -3844,6 +3842,7 @@ static void Luks2Reencryption(void)
 		.hash = "sha1",
 		.luks2 = &params2,
 	};
+	dev_t devno;
 
 	const char *mk_hex = "bb21babe733229347bd4e681891e213d94c685be6a5b84818afe7a78a6de7a1a";
 	size_t key_size = strlen(mk_hex) / 2;
@@ -4354,6 +4353,8 @@ static void Luks2Reencryption(void)
 	EQ_(crypt_activate_by_passphrase(cd, CDEVICE_2, 6, PASSPHRASE, strlen(PASSPHRASE), 0), 6);
 	OK_(t_device_size(DMDIR CDEVICE_2, &r_size_1));
 	EQ_(r_size_1, 512);
+	// store devno for later size check
+	OK_(t_get_devno(CDEVICE_2, &devno));
 	// create placeholder device to block automatic deactivation after decryption
 	OK_(_system("dmsetup create " CDEVICE_1 " --table \"0 1 linear " DMDIR CDEVICE_2 " 0\"", 1));
 	remove(BACKUP_FILE);
@@ -4373,7 +4374,7 @@ static void Luks2Reencryption(void)
 	EQ_(crypt_get_data_offset(cd), 0);
 	OK_(crypt_reencrypt_run(cd, NULL, NULL));
 	remove(BACKUP_FILE);
-	OK_(t_device_size(DMDIR CDEVICE_2, &r_size_1));
+	OK_(t_device_size_by_devno(devno, &r_size_1));
 	EQ_(r_size_1, 512);
 	OK_(_system("dmsetup remove " DM_RETRY CDEVICE_1 DM_NOSTDERR, 0));
 	CRYPT_FREE(cd);
diff --git a/tests/api-test.c b/tests/api-test.c
index 258c24be..93ac8e08 100644
--- a/tests/api-test.c
+++ b/tests/api-test.c
@@ -34,8 +34,6 @@
 #include "luks1/luks.h"
 #include "libcryptsetup.h"
 
-#define DMDIR "/dev/mapper/"
-
 #define DEVICE_1_UUID "28632274-8c8a-493f-835b-da802e1c576b"
 #define DEVICE_EMPTY_name "crypt_zero"
 #define DEVICE_EMPTY DMDIR DEVICE_EMPTY_name
diff --git a/tests/api_test.h b/tests/api_test.h
index fef03664..f9109e5c 100644
--- a/tests/api_test.h
+++ b/tests/api_test.h
@@ -96,6 +96,8 @@ void xlog(const char *msg, const char *tst, const char *func, int line, const ch
 
 #define CRYPT_FREE(x) do { crypt_free(x); x = NULL; } while (0)
 
+#define DMDIR "/dev/mapper/"
+
 #define TST_SECTOR_SHIFT 9L
 #define TST_SECTOR_SIZE 512
 #define TST_LOOP_FILE_SIZE (((1 << 20) * 100) >> TST_SECTOR_SHIFT)
@@ -124,4 +126,7 @@ int loop_attach(char **loop, const char *file, int offset,
 		      int autoclear, int *readonly);
 int loop_detach(const char *loop);
 
+int t_device_size_by_devno(dev_t devno, uint64_t *retval);
+int t_get_devno(const char *dev, dev_t *devno);
+
 #endif
diff --git a/tests/test_utils.c b/tests/test_utils.c
index 213581e3..9f4a6334 100644
--- a/tests/test_utils.c
+++ b/tests/test_utils.c
@@ -684,3 +684,60 @@ int loop_detach(const char *loop)
 	close(loop_fd);
 	return r;
 }
+
+int t_get_devno(const char *name, dev_t *devno)
+{
+	char path[PATH_MAX];
+	int r;
+	struct stat st;
+
+	r = snprintf(path, sizeof(path), DMDIR "%s", name);
+	if (r < 0 || (size_t)r >= sizeof(path))
+		return 1;
+
+	if (stat(path, &st) || !S_ISBLK(st.st_mode))
+		return 1;
+
+	*devno = st.st_rdev;
+
+	return 0;
+}
+
+static int _read_uint64(const char *sysfs_path, uint64_t *value)
+{
+        char tmp[64] = {0};
+        int fd, r;
+
+        if ((fd = open(sysfs_path, O_RDONLY)) < 0)
+                return 0;
+        r = read(fd, tmp, sizeof(tmp));
+        close(fd);
+
+        if (r <= 0)
+                return 0;
+
+        if (sscanf(tmp, "%" PRIu64, value) != 1)
+                return 0;
+
+        return 1;
+}
+
+static int _sysfs_get_uint64(int major, int minor, uint64_t *value, const char *attr)
+{
+        char path[PATH_MAX];
+
+        if (snprintf(path, sizeof(path), "/sys/dev/block/%d:%d/%s",
+                     major, minor, attr) < 0)
+                return 0;
+
+        return _read_uint64(path, value);
+}
+
+int t_device_size_by_devno(dev_t devno, uint64_t *retval)
+{
+	if (!_sysfs_get_uint64(major(devno), minor(devno), retval, "size"))
+		return 1;
+
+	*retval *= 512;
+	return 0;
+}