diff --git a/src/ens/ens_error.h b/src/ens/ens_error.h
new file mode 100644
index 0000000..213ce22
--- /dev/null
+++ b/src/ens/ens_error.h
@@ -0,0 +1,8 @@
+#ifndef ENS_ERROR_H
+#define ENS_ERROR_H
+
+#define ENS_INTERR  1 // internal error
+#define ENS_NOENT   2 // entry not found or invalid
+#define ENS_INVARG  3 // invalid argument
+
+#endif
\ No newline at end of file
diff --git a/src/ens/ens_fs.c b/src/ens/ens_fs.c
index 8d51d4b..f4bcfbe 100644
--- a/src/ens/ens_fs.c
+++ b/src/ens/ens_fs.c
@@ -4,71 +4,73 @@
 #include <string.h>
 
 #include "ens_fs.h"
+#include "ens_error.h"
 
 #define SEED 42
 
 int ens_fs_init(ens_fs_t* fs, uint8_t id, uint64_t entry_size) {
-    int rc = flash_area_open(id, &fs->area);
-    if (rc) {
-        goto end;
+    if (flash_area_open(id, &fs->area)) {
+        // opening of flash area was not successful
+        return -ENS_INTERR;
     }
 
-    // Check, if entry size is multiple of flash_area_align
+    // check, if entry size is multiple of flash_area_align
     if((entry_size % flash_area_align(fs->area)) != 0) {
         flash_area_close(fs->area);
-        // TODO lome: set custom error code
-        rc = -1;
-        goto end;
+        return -ENS_INVARG;
     }
     fs->entry_size = entry_size;
 
+    // get all information needed for the needed for the fs
     const struct device* dev = flash_area_get_device(fs->area);
-
     fs->sector_count = flash_get_page_count(dev);
     struct flash_pages_info info;
-    rc = flash_get_page_info_by_offs(dev, fs->area->fa_off, &info);
+    if (flash_get_page_info_by_offs(dev, fs->area->fa_off, &info)) {
+        // on error, close the flash area
+        flash_area_close(&fs->area);
+        return -ENS_INTERR;
+    }
     fs->sector_size = info.size;
 
-end:
-    return rc;
+    return 0;
 }
 
 int ens_fs_read(ens_fs_t* fs, uint64_t id, void* dist) {
 
+    // read the entry from flash
     uint64_t offset = id * fs->entry_size;
-
-    int rc = flash_area_read(fs->area, offset, dist, fs->entry_size);
-    if(rc) {
-       goto end;
+    if(flash_area_read(fs->area, offset, dist, fs->entry_size)) {
+        // opening of flash area was not successful
+        return -ENS_INTERR;
     }
 
+    // check, if checksum and not-deleted flag are as expected
     uint8_t* obj = dist;
     uint8_t metadata = crc7_be(SEED, obj, fs->entry_size - 1) | 1;
     int isInvalid = memcmp(&obj[fs->entry_size - 1], &metadata, 1);
     if(isInvalid) {
-        // If checksum is not equal to calculated checksum or if deleted flag is not 1, set memory to 0
-        rc = -1;
+        // if checksum is not equal to calculated checksum or if deleted flag is not 1, set memory to 0
         memset(dist, 0, fs->entry_size);
+        // we do not know, if object got deleted or data is corrupt
+        return -ENS_NOENT;
     }
-end:
 
-    return rc;
+    return 0;
 }
 
 int ens_fs_write(ens_fs_t* fs, uint64_t id, void* data) {
 
-    // Set CRC and not-deleted-flag
+    // set CRC and not-deleted-flag
     uint8_t* obj = data;
     obj[fs->entry_size - 1] = crc7_be(SEED, obj, fs->entry_size - 1) | 1;
 
     uint64_t offset = id * fs->entry_size;
-    int rc = flash_area_write(fs->area, offset, data, fs->entry_size);
-    if(rc) {
-        goto end;
+    if(flash_area_write(fs->area, offset, data, fs->entry_size)) {
+        // writing to flash was not successful
+        return -ENS_INTERR;
     }
 
-end:
-    return rc;
+    return 0;
 }
 
 int ens_fs_delete(ens_fs_t* fs, uint64_t id) {
@@ -76,23 +78,30 @@ int ens_fs_delete(ens_fs_t* fs, uint64_t id) {
     uint8_t data[fs->entry_size];
 
     uint64_t offset = id * fs->entry_size;
-    int rc = flash_area_read(fs->area, offset, data, fs->entry_size);
-    if(rc) {
-        goto end;
+    if(flash_area_read(fs->area, offset, data, fs->entry_size)) {
+        // reading was not successful
+        return -ENS_INTERR;
     }
 
     // set memory to 0, so not-deleted flag is 0
     memset(data, 0, fs->entry_size);
-    rc = flash_area_write(fs->area, offset, data, fs->entry_size);
+    if(flash_area_write(fs->area, offset, data, fs->entry_size)) {
+        // writing was not successful
+        return -ENS_INTERR;
+    }
 
-end:
-    return rc;
+    return 0;
 }
 
 int ens_fs_page_erase(ens_fs_t* fs, uint64_t offset, uint64_t sector_count) {
+
+    // calculate the next page start before (or at) the given offset
     uint64_t start = (offset - offset % fs->sector_size) * fs->entry_size;
 
-    int rc = flash_area_erase(fs->area, start, fs->sector_size * sector_count);
+    // erase given amount of pages, starting for the given offset
+    if(flash_area_erase(fs->area, start, fs->sector_size * sector_count)) {
+        return -ENS_INTERR;
+    }
 
-    return rc;
+    return 0;
 }
diff --git a/src/ens/storage.c b/src/ens/storage.c
index 62ee81d..68498bb 100644
--- a/src/ens/storage.c
+++ b/src/ens/storage.c
@@ -111,7 +111,7 @@ int load_contact(record_t* dest, record_sequence_number_t sn) {
     storage_id_t id = convert_sn_to_storage_id(sn);
     // int rc = nvs_read(&info_fs, id, dest, sizeof(*dest));
     int rc = ens_fs_read(&ens_fs, id, dest);
-    if (rc <= 0) {
+    if (rc < 0) {
         return rc;
     }
     return 0;
@@ -132,11 +132,7 @@ int add_contact(record_t* src) {
     src->sn = curr_sn;
     storage_id_t id = convert_sn_to_storage_id(curr_sn);
 
-    int rc = ens_fs_write(&ens_fs, id, src);
-    if (rc > 0) {
-        return 0;
-    }
-    return rc;
+    return ens_fs_write(&ens_fs, id, src);
 }
 
 int delete_contact(record_sequence_number_t sn) {