diff --git a/postinstall_runner_action.cc b/postinstall_runner_action.cc
index 6be13e1..f8bcc36 100644
--- a/postinstall_runner_action.cc
+++ b/postinstall_runner_action.cc
@@ -18,7 +18,13 @@
 using std::vector;
 
 namespace {
+// The absolute path to the post install command.
 const char kPostinstallScript[] = "/postinst";
+
+// Path to the binary file used by kPostinstallScript. Used to get and log the
+// file format of the binary to debug issues when the ELF format on the update
+// doesn't match the one on the current system. This path is not executed.
+const char kDebugPostinstallBinaryPath[] = "/usr/bin/cros_installer";
 }
 
 void PostinstallRunnerAction::PerformAction() {
@@ -66,6 +72,15 @@
     }
   }
 
+  // Logs the file format of the postinstall script we are about to run. This
+  // will help debug when the postinstall script doesn't match the architecture
+  // of our build.
+  LOG(INFO) << "Format file for new " <<  kPostinstallScript << " is: "
+            << utils::GetFileFormat(temp_rootfs_dir_ + kPostinstallScript);
+  LOG(INFO) << "Format file for new " <<  kDebugPostinstallBinaryPath << " is: "
+            << utils::GetFileFormat(
+                temp_rootfs_dir_ + kDebugPostinstallBinaryPath);
+
   // Runs the postinstall script asynchronously to free up the main loop while
   // it's running.
   vector<string> command;
diff --git a/utils.cc b/utils.cc
index 7558f35..70b9c75 100644
--- a/utils.cc
+++ b/utils.cc
@@ -56,6 +56,11 @@
 // one second.
 const int kUnmountMaxNumOfRetries = 5;
 const int kUnmountRetryIntervalInMicroseconds = 200 * 1000;  // 200 ms
+
+// Number of bytes to read from a file to attempt to detect its contents. Used
+// in GetFileFormat.
+const int kGetFileFormatMaxHeaderSize = 32;
+
 }  // namespace
 
 namespace utils {
@@ -665,6 +670,83 @@
   return true;
 }
 
+// Tries to parse the header of an ELF file to obtain a human-readable
+// description of it on the |output| string.
+static bool GetFileFormatELF(const char* buffer, size_t size, string* output) {
+  // 0x00: EI_MAG - ELF magic header, 4 bytes.
+  if (size < 4 || memcmp(buffer, "\x7F""ELF", 4) != 0)
+    return false;
+  *output = "ELF";
+
+  // 0x04: EI_CLASS, 1 byte.
+  if (size < 0x04 + 1)
+    return true;
+  switch (buffer[4]) {
+    case 1:
+      *output += " 32-bit";
+      break;
+    case 2:
+      *output += " 64-bit";
+      break;
+    default:
+      *output += " ?-bit";
+  }
+
+  // 0x05: EI_DATA, endianness, 1 byte.
+  if (size < 0x05 + 1)
+    return true;
+  char ei_data = buffer[5];
+  switch (ei_data) {
+    case 1:
+      *output += " little-endian";
+      break;
+    case 2:
+      *output += " big-endian";
+      break;
+    default:
+      *output += " ?-endian";
+      // Don't parse anything after the 0x10 offset if endianness is unknown.
+      return true;
+  }
+
+  // 0x12: e_machine, 2 byte endianness based on ei_data
+  if (size < 0x12 + 2)
+    return true;
+  uint16 e_machine = *reinterpret_cast<const uint16*>(buffer+0x12);
+  // Fix endianess regardless of the host endianess.
+  if (ei_data == 1)
+    e_machine = le16toh(e_machine);
+  else
+    e_machine = be16toh(e_machine);
+
+  switch (e_machine) {
+    case 0x03:
+      *output += " x86";
+      break;
+    case 0x28:
+      *output += " arm";
+      break;
+    case 0x3E:
+      *output += " x86-64";
+      break;
+    default:
+      *output += " unknown-arch";
+  }
+  return true;
+}
+
+string GetFileFormat(const string& path) {
+  vector<char> buffer;
+  if (!ReadFileChunkAndAppend(path, 0, kGetFileFormatMaxHeaderSize, &buffer))
+    return "File not found.";
+
+  string result;
+  if (GetFileFormatELF(buffer.data(), buffer.size(), &result))
+    return result;
+
+  return "data";
+}
+
 bool GetBootloader(BootLoader* out_bootloader) {
   // For now, hardcode to syslinux.
   *out_bootloader = BootLoader_SYSLINUX;
diff --git a/utils.h b/utils.h
index f404653..e129cbe 100644
--- a/utils.h
+++ b/utils.h
@@ -193,6 +193,11 @@
                              int* out_block_count,
                              int* out_block_size);
 
+
+// Returns a human-readable string with the file format based on magic constants
+// on the header of the file.
+std::string GetFileFormat(const std::string& path);
+
 // Returns the string representation of the given UTC time.
 // such as "11/14/2011 14:05:30 GMT".
 std::string ToString(const base::Time utc_time);
diff --git a/utils_unittest.cc b/utils_unittest.cc
index d75a6b0..ef771b9 100644
--- a/utils_unittest.cc
+++ b/utils_unittest.cc
@@ -327,6 +327,48 @@
 }
 
 namespace {
+void GetFileFormatTester(const string& expected,
+                         const vector<uint8>& contents) {
+  ScopedTempFile file;
+  ASSERT_TRUE(utils::WriteFile(file.GetPath().c_str(),
+                               reinterpret_cast<const char*>(contents.data()),
+                               contents.size()));
+  EXPECT_EQ(expected, utils::GetFileFormat(file.GetPath()));
+}
+}
+
+TEST(UtilsTest, GetFileFormatTest) {
+  EXPECT_EQ("File not found.", utils::GetFileFormat("/path/to/nowhere"));
+  GetFileFormatTester("data", vector<uint8>{1, 2, 3, 4, 5, 6, 7, 8});
+  GetFileFormatTester("ELF", vector<uint8>{0x7f, 0x45, 0x4c, 0x46});
+
+  // Real tests from cros_installer on different boards.
+  // ELF 32-bit LSB executable, Intel 80386
+  GetFileFormatTester(
+      "ELF 32-bit little-endian x86",
+      vector<uint8>{0x7f, 0x45, 0x4c, 0x46, 0x01, 0x01, 0x01, 0x00,
+                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+                    0x02, 0x00, 0x03, 0x00, 0x01, 0x00, 0x00, 0x00,
+                    0x90, 0x83, 0x04, 0x08, 0x34, 0x00, 0x00, 0x00});
+
+  // ELF 32-bit LSB executable, ARM
+  GetFileFormatTester(
+      "ELF 32-bit little-endian arm",
+      vector<uint8>{0x7f, 0x45, 0x4c, 0x46, 0x01, 0x01, 0x01, 0x00,
+                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+                    0x02, 0x00, 0x28, 0x00, 0x01, 0x00, 0x00, 0x00,
+                    0x85, 0x8b, 0x00, 0x00, 0x34, 0x00, 0x00, 0x00});
+
+  // ELF 64-bit LSB executable, x86-64
+  GetFileFormatTester(
+      "ELF 64-bit little-endian x86-64",
+      vector<uint8>{0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00,
+                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+                    0x02, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00,
+                    0xb0, 0x04, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00});
+}
+
+namespace {
 gboolean  TerminateScheduleCrashReporterUploadTest(void* arg) {
   GMainLoop* loop = reinterpret_cast<GMainLoop*>(arg);
   g_main_loop_quit(loop);