diff --git a/common/utils_unittest.cc b/common/utils_unittest.cc
index b5887e3..eaae023 100644
--- a/common/utils_unittest.cc
+++ b/common/utils_unittest.cc
@@ -16,7 +16,9 @@
 
 #include "update_engine/common/utils.h"
 
+#include <fcntl.h>
 #include <stdint.h>
+#include <sys/mount.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
@@ -441,4 +443,37 @@
   EXPECT_TRUE(BoolMacroTestHelper());
 }
 
+TEST(UtilsTest, UnmountFilesystemFailureTest) {
+  EXPECT_FALSE(utils::UnmountFilesystem("/path/to/non-existing-dir"));
+}
+
+TEST(UtilsTest, UnmountFilesystemBusyFailureTest) {
+  string tmp_image;
+  EXPECT_TRUE(utils::MakeTempFile("img.XXXXXX", &tmp_image, nullptr));
+  ScopedPathUnlinker tmp_image_unlinker(tmp_image);
+
+  EXPECT_TRUE(base::CopyFile(
+      test_utils::GetBuildArtifactsPath().Append("gen/disk_ext2_4k.img"),
+      base::FilePath(tmp_image)));
+
+  base::ScopedTempDir mnt_dir;
+  EXPECT_TRUE(mnt_dir.CreateUniqueTempDir());
+
+  string loop_dev;
+  test_utils::ScopedLoopbackDeviceBinder loop_binder(
+      tmp_image, true, &loop_dev);
+
+  // This is the actual test part. While we hold a file descriptor open for the
+  // mounted filesystem, umount should still succeed.
+  EXPECT_TRUE(utils::MountFilesystem(
+      loop_dev, mnt_dir.path().value(), MS_RDONLY, "ext4", ""));
+  string target_file = mnt_dir.path().Append("empty-file").value();
+  int fd = HANDLE_EINTR(open(target_file.c_str(), O_RDONLY));
+  EXPECT_GE(fd, 0);
+  EXPECT_TRUE(utils::UnmountFilesystem(mnt_dir.path().value()));
+  IGNORE_EINTR(close(fd));
+  // The filesystem was already unmounted so this call should fail.
+  EXPECT_FALSE(utils::UnmountFilesystem(mnt_dir.path().value()));
+}
+
 }  // namespace chromeos_update_engine