diff --git a/filesystem_iterator_unittest.cc b/filesystem_iterator_unittest.cc
index aca95ff..aed16e5 100644
--- a/filesystem_iterator_unittest.cc
+++ b/filesystem_iterator_unittest.cc
@@ -57,9 +57,9 @@
   set<string> expected_paths(expected_paths_vector.begin(),
                              expected_paths_vector.end());
   VerifyAllPaths(kMountPath, expected_paths);
-  
-  EXPECT_EQ(0, System(string("umount ") + kMountPath + "/some_dir/mnt"));
-  EXPECT_EQ(0, System(string("umount ") + kMountPath));
+
+  EXPECT_TRUE(utils::UnmountFilesystem(kMountPath + string("/some_dir/mnt")));
+  EXPECT_TRUE(utils::UnmountFilesystem(kMountPath));
   EXPECT_EQ(0, System(string("rm -f ") + first_image + " " + sub_image));
 }
 
diff --git a/postinstall_runner_action_unittest.cc b/postinstall_runner_action_unittest.cc
index 8f42ddd..65f378e 100644
--- a/postinstall_runner_action_unittest.cc
+++ b/postinstall_runner_action_unittest.cc
@@ -119,7 +119,7 @@
   ASSERT_TRUE(WriteFileString(mountpoint + "/postinst", script));
   ASSERT_EQ(0, System(string("chmod a+x ") + mountpoint + "/postinst"));
 
-  ASSERT_EQ(0, System(string("umount ") + mountpoint));
+  ASSERT_TRUE(utils::UnmountFilesystem(mountpoint));
 
   ASSERT_EQ(0, System(string("rm -f ") + cwd + "/postinst_called"));
 
diff --git a/test_utils.cc b/test_utils.cc
index fddd2d1..5379979 100644
--- a/test_utils.cc
+++ b/test_utils.cc
@@ -217,7 +217,7 @@
                                    kMountPath, kMountPath)));
   EXPECT_EQ(0, System(StringPrintf("ln -s bogus %s/boguslink",
                                    kMountPath)));
-  EXPECT_EQ(0, System(StringPrintf("umount %s", kMountPath)));
+  EXPECT_TRUE(utils::UnmountFilesystem(kMountPath));
 
   if (out_paths) {
     out_paths->clear();
diff --git a/utils.cc b/utils.cc
index e0d9244..1e87262 100644
--- a/utils.cc
+++ b/utils.cc
@@ -41,6 +41,16 @@
 
 namespace chromeos_update_engine {
 
+namespace {
+
+// The following constants control how UnmountFilesystem should retry if
+// umount() fails with an errno EBUSY, i.e. retry 5 times over the course of
+// one second.
+const int kUnmountMaxNumOfRetries = 5;
+const int kUnmountRetryIntervalInMicroseconds = 200 * 1000;  // 200 ms
+
+}  // namespace
+
 namespace utils {
 
 static const char kDevImageMarker[] = "/root/.dev_mode";
@@ -497,7 +507,14 @@
 }
 
 bool UnmountFilesystem(const string& mountpoint) {
-  TEST_AND_RETURN_FALSE_ERRNO(umount(mountpoint.c_str()) == 0);
+  for (int num_retries = 0; ; ++num_retries) {
+    if (umount(mountpoint.c_str()) == 0)
+      break;
+
+    TEST_AND_RETURN_FALSE_ERRNO(errno == EBUSY &&
+                                num_retries < kUnmountMaxNumOfRetries);
+    usleep(kUnmountRetryIntervalInMicroseconds);
+  }
   return true;
 }