diff --git a/postinstall_runner_action.cc b/postinstall_runner_action.cc
index c6320e1..80c28c9 100644
--- a/postinstall_runner_action.cc
+++ b/postinstall_runner_action.cc
@@ -32,11 +32,11 @@
   unsigned long mountflags = MS_RDONLY;
   int rc = mount(install_device.c_str(),
                  temp_rootfs_dir_.c_str(),
-                 "ext4",
+                 "ext2",
                  mountflags,
                  NULL);
   if (rc < 0) {
-    LOG(INFO) << "Failed to mount install part as ext4. Trying ext3.";
+    LOG(INFO) << "Failed to mount install part as ext2. Trying ext3.";
     rc = mount(install_device.c_str(),
                temp_rootfs_dir_.c_str(),
                "ext3",
diff --git a/postinstall_runner_action_unittest.cc b/postinstall_runner_action_unittest.cc
index 7f4e65c..baf03b6 100644
--- a/postinstall_runner_action_unittest.cc
+++ b/postinstall_runner_action_unittest.cc
@@ -5,9 +5,13 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+
 #include <string>
 #include <vector>
+
+#include <base/string_util.h>
 #include <gtest/gtest.h>
+
 #include "update_engine/postinstall_runner_action.h"
 #include "update_engine/test_utils.h"
 #include "update_engine/utils.h"
@@ -90,14 +94,19 @@
   ASSERT_EQ(0, system("dd if=/dev/zero of=image.dat seek=10485759 bs=1 "
                       "count=1"));
 
-  // format it as ext3
-  ASSERT_EQ(0, system("mkfs.ext3 -F image.dat"));
+  // format it as ext2
+  ASSERT_EQ(0, system("mkfs.ext2 -F image.dat"));
 
   // mount it
   ASSERT_EQ(0, System(string("mount -o loop image.dat ") + mountpoint));
 
   // put a postinst script in
-  string script = string("#!/bin/bash\ntouch ") + cwd + "/postinst_called\n";
+  string script = StringPrintf("#!/bin/bash\n"
+                               "mount | grep au_postint_mount | grep ext2\n"
+                               "if [ $? -eq 0 ]; then\n"
+                               "  touch %s/postinst_called\n"
+                               "fi\n",
+                               cwd.c_str());
   if (do_err_script) {
     script = "#!/bin/bash\nexit 1";
   }