diff --git a/CHANGELOG.md b/CHANGELOG.md
index 12ec77526cc57f0f042d74aeef17bd971454e1ce..1db35e7339e9f4540f0cc955e28246c953615236 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Additional tests to increase code coverage ([!141](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/141)).
 - GKFS_ENABLE_UNUSED_FUNCTIONS added to disable code to increase code coverage.
 - Updated Parallax version to new API (parallax option needs kv_format.parallax in the path, and the database in a device with O_DIRECT)
+- Support for increasing file size via `truncate()` added ([!159](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/159)
 
 ### Changed
 
diff --git a/src/client/gkfs_functions.cpp b/src/client/gkfs_functions.cpp
index 23db5e0f0a055530bcff78b607e12a5b6662f74f..95a09f1c105224c4f288fbf116c2995522bf90e4 100644
--- a/src/client/gkfs_functions.cpp
+++ b/src/client/gkfs_functions.cpp
@@ -143,6 +143,7 @@ gkfs_open(const std::string& path, mode_t mode, int flags) {
         errno = ENOTSUP;
         return -1;
     }
+
     // metadata object filled during create or stat
     gkfs::metadata::Metadata md{};
     if(flags & O_CREAT) {
@@ -578,9 +579,27 @@ gkfs_truncate(const std::string& path, off_t length) {
 
     auto size = md->size();
     if(static_cast<unsigned long>(length) > size) {
-        LOG(DEBUG, "Length is greater then file size: {} > {}", length, size);
-        errno = EINVAL;
-        return -1;
+        LOG(DEBUG, "Length is greater then file size: '{}' > '{}'", length,
+            size);
+        auto output_fd = gkfs_open(path, md->mode(), O_WRONLY);
+        if(output_fd == -1) {
+            errno = EINVAL;
+            return -1;
+        }
+        gkfs_lseek(output_fd, 0, SEEK_END);
+        ssize_t n = static_cast<unsigned long>(length) - size;
+        // Zeroes the buffer. All make_* are value initialized
+        auto buf = std::make_unique<char[]>(n);
+        if(!buf) {
+            errno = ENOMEM;
+            return -1;
+        }
+        if(gkfs_write(output_fd, buf.get(), (size_t) n) != n) {
+            errno = EINVAL;
+            return -1;
+        }
+        CTX->file_map()->remove(output_fd);
+        return 0;
     }
     return gkfs_truncate(path, size, length);
 }
@@ -677,8 +696,10 @@ ssize_t
 gkfs_write(int fd, const void* buf, size_t count) {
     auto gkfs_fd = CTX->file_map()->get(fd);
     auto pos = gkfs_fd->pos(); // retrieve the current offset
-    if(gkfs_fd->get_flag(gkfs::filemap::OpenFile_flags::append))
+    if(gkfs_fd->get_flag(gkfs::filemap::OpenFile_flags::append)) {
         gkfs_lseek(gkfs_fd, 0, SEEK_END);
+        pos = gkfs_fd->pos(); // Pos should be updated with append
+    }
     auto ret = gkfs_pwrite(gkfs_fd, reinterpret_cast<const char*>(buf), count,
                            pos);
     // Update offset in file descriptor in the file map
diff --git a/tests/integration/data/test_truncate.py b/tests/integration/data/test_truncate.py
index 4d6fc40da3d758defd848bce889f46a33f9809dd..b1321dfdce127ede0931588766635ff8c932644a 100644
--- a/tests/integration/data/test_truncate.py
+++ b/tests/integration/data/test_truncate.py
@@ -150,7 +150,11 @@ def test_fail_truncate(gkfs_daemon, gkfs_client):
 
     # Truncate to a size greater than the file size
     ret = gkfs_client.truncate(truncfile, buf_length + 1)
-    assert ret.retval == -1
-    assert ret.errno == errno.EINVAL
+    assert ret.retval == 0
+
+    
+    # Size should increase
+    ret = gkfs_client.stat(truncfile)
+    assert ret.statbuf.st_size == buf_length+1