diff --git a/cmds/idmap2/tests/FabricatedOverlayTests.cpp b/cmds/idmap2/tests/FabricatedOverlayTests.cpp
index 6b1c7e8..15109d9 100644
--- a/cmds/idmap2/tests/FabricatedOverlayTests.cpp
+++ b/cmds/idmap2/tests/FabricatedOverlayTests.cpp
@@ -144,7 +144,7 @@
               "com.example.target:string/string1", Res_value::TYPE_STRING, "foobar", "")
           .Build();
   ASSERT_TRUE(overlay);
-  TemporaryFile tf;
+  TempFrroFile tf;
   std::ofstream out(tf.path);
   ASSERT_TRUE((*overlay).ToBinaryStream(out));
   out.close();
diff --git a/cmds/idmap2/tests/IdmapTests.cpp b/cmds/idmap2/tests/IdmapTests.cpp
index a384305..c85619c 100644
--- a/cmds/idmap2/tests/IdmapTests.cpp
+++ b/cmds/idmap2/tests/IdmapTests.cpp
@@ -274,7 +274,7 @@
                   .Build();
 
   ASSERT_TRUE(frro);
-  TemporaryFile tf;
+  TempFrroFile tf;
   std::ofstream out(tf.path);
   ASSERT_TRUE((*frro).ToBinaryStream(out));
   out.close();
@@ -467,9 +467,9 @@
 TEST(IdmapTests, IdmapHeaderIsUpToDate) {
   fclose(stderr);  // silence expected warnings from libandroidfw
 
-  const std::string target_apk_path = kIdmapRawTargetPath;
-  const std::string overlay_apk_path = kIdmapRawOverlayPath;
-  const std::string overlay_name = kIdmapRawOverlayName;
+  const std::string target_apk_path {kIdmapRawTargetPath};
+  const std::string overlay_apk_path {kIdmapRawOverlayPath};
+  const std::string overlay_name {kIdmapRawOverlayName};
   const PolicyBitmask policies = kIdmapRawDataPolicies;
   const uint32_t target_crc = kIdmapRawDataTargetCrc;
   const uint32_t overlay_crc = kIdmapRawOverlayCrc;
diff --git a/cmds/idmap2/tests/ResourceMappingTests.cpp b/cmds/idmap2/tests/ResourceMappingTests.cpp
index db44c23..1d22553 100644
--- a/cmds/idmap2/tests/ResourceMappingTests.cpp
+++ b/cmds/idmap2/tests/ResourceMappingTests.cpp
@@ -217,7 +217,7 @@
                   .Build();
 
   ASSERT_TRUE(frro);
-  TemporaryFile tf;
+  TempFrroFile tf;
   std::ofstream out(tf.path);
   ASSERT_TRUE((*frro).ToBinaryStream(out));
   out.close();
diff --git a/cmds/idmap2/tests/TestHelpers.h b/cmds/idmap2/tests/TestHelpers.h
index cdc0b8f..bf01c32 100644
--- a/cmds/idmap2/tests/TestHelpers.h
+++ b/cmds/idmap2/tests/TestHelpers.h
@@ -17,11 +17,15 @@
 #ifndef IDMAP2_TESTS_TESTHELPERS_H_
 #define IDMAP2_TESTS_TESTHELPERS_H_
 
+#include <stdio.h>
 #include <string>
+#include <string_view>
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
+#include "android-base/file.h"
+
 namespace android::idmap2 {
 
 const unsigned char kIdmapRawData[] = {
@@ -197,12 +201,23 @@
 const unsigned int kIdmapRawDataTargetCrc = 0x1234;
 const unsigned int kIdmapRawOverlayCrc = 0x5678;
 const unsigned int kIdmapRawDataPolicies = 0x11;
-inline const std::string kIdmapRawTargetPath = "targetX.apk";
-inline const std::string kIdmapRawOverlayPath = "overlayX.apk";
-inline const std::string kIdmapRawOverlayName = "OverlayName";
+inline const std::string_view kIdmapRawTargetPath = "targetX.apk";
+inline const std::string_view kIdmapRawOverlayPath = "overlayX.apk";
+inline const std::string_view kIdmapRawOverlayName = "OverlayName";
 
 std::string GetTestDataPath();
 
+class TempFrroFile : public TemporaryFile {
+public:
+  TempFrroFile() {
+    std::string new_path = path;
+    new_path += ".frro";
+    ::rename(path, new_path.c_str());
+    const auto new_len = new_path.copy(path, sizeof(path) - 1);
+    path[new_len] = '\0';
+  }
+};
+
 class Idmap2Tests : public testing::Test {
  protected:
   void SetUp() override {
diff --git a/libs/androidfw/ApkAssets.cpp b/libs/androidfw/ApkAssets.cpp
index f0c6395..49254d1 100644
--- a/libs/androidfw/ApkAssets.cpp
+++ b/libs/androidfw/ApkAssets.cpp
@@ -81,7 +81,7 @@
   std::string overlay_path(loaded_idmap->OverlayApkPath());
   auto fd = unique_fd(base::utf8::open(overlay_path.c_str(), O_RDONLY | O_CLOEXEC));
   std::unique_ptr<AssetsProvider> overlay_assets;
-  if (IsFabricatedOverlay(fd)) {
+  if (IsFabricatedOverlayName(overlay_path) && IsFabricatedOverlay(fd)) {
     // Fabricated overlays do not contain resource definitions. All of the overlay resource values
     // are defined inline in the idmap.
     overlay_assets = EmptyAssetsProvider::Create(std::move(overlay_path));
@@ -137,8 +137,7 @@
       return {};
     }
     loaded_arsc = LoadedArsc::Load(data, length, loaded_idmap.get(), property_flags);
-  } else if (loaded_idmap != nullptr &&
-      IsFabricatedOverlay(std::string(loaded_idmap->OverlayApkPath()))) {
+  } else if (loaded_idmap != nullptr && IsFabricatedOverlay(loaded_idmap->OverlayApkPath())) {
     loaded_arsc = LoadedArsc::Load(loaded_idmap.get());
   } else {
     loaded_arsc = LoadedArsc::CreateEmpty();
diff --git a/libs/androidfw/Idmap.cpp b/libs/androidfw/Idmap.cpp
index 5f98b8f..9824190 100644
--- a/libs/androidfw/Idmap.cpp
+++ b/libs/androidfw/Idmap.cpp
@@ -18,8 +18,10 @@
 
 #include "androidfw/Idmap.h"
 
+#include "android-base/file.h"
 #include "android-base/logging.h"
 #include "android-base/stringprintf.h"
+#include "android-base/utf8.h"
 #include "androidfw/misc.h"
 #include "androidfw/ResourceTypes.h"
 #include "androidfw/Util.h"
@@ -250,7 +252,12 @@
 }
 } // namespace
 
-LoadedIdmap::LoadedIdmap(std::string&& idmap_path, const Idmap_header* header,
+// O_PATH is a lightweight way of creating an FD, only exists on Linux
+#ifndef O_PATH
+#define O_PATH (0)
+#endif
+
+LoadedIdmap::LoadedIdmap(const std::string& idmap_path, const Idmap_header* header,
                          const Idmap_data_header* data_header,
                          const Idmap_target_entry* target_entries,
                          const Idmap_target_entry_inline* target_inline_entries,
@@ -267,10 +274,10 @@
       configurations_(configs),
       overlay_entries_(overlay_entries),
       string_pool_(std::move(string_pool)),
-      idmap_path_(std::move(idmap_path)),
+      idmap_fd_(android::base::utf8::open(idmap_path.c_str(), O_RDONLY|O_CLOEXEC|O_BINARY|O_PATH)),
       overlay_apk_path_(overlay_apk_path),
       target_apk_path_(target_apk_path),
-      idmap_last_mod_time_(getFileModDate(idmap_path_.data())) {}
+      idmap_last_mod_time_(getFileModDate(idmap_fd_.get())) {}
 
 std::unique_ptr<LoadedIdmap> LoadedIdmap::Load(StringPiece idmap_path, StringPiece idmap_data) {
   ATRACE_CALL();
@@ -368,7 +375,7 @@
 }
 
 bool LoadedIdmap::IsUpToDate() const {
-  return idmap_last_mod_time_ == getFileModDate(idmap_path_.c_str());
+  return idmap_last_mod_time_ == getFileModDate(idmap_fd_.get());
 }
 
 }  // namespace android
diff --git a/libs/androidfw/ResourceTypes.cpp b/libs/androidfw/ResourceTypes.cpp
index 2c99f1a..a3dd983 100644
--- a/libs/androidfw/ResourceTypes.cpp
+++ b/libs/androidfw/ResourceTypes.cpp
@@ -54,6 +54,8 @@
 #define INT32_MAX ((int32_t)(2147483647))
 #endif
 
+using namespace std::literals;
+
 namespace android {
 
 #if defined(_WIN32)
@@ -237,12 +239,24 @@
     fill9patchOffsets(reinterpret_cast<Res_png_9patch*>(outData));
 }
 
-bool IsFabricatedOverlay(const std::string& path) {
-  return IsFabricatedOverlay(path.c_str());
+bool IsFabricatedOverlayName(std::string_view path) {
+  static constexpr auto suffixFrro = ".frro"sv;
+  static constexpr auto suffixIdmap = ".frro@idmap"sv;
+
+  return (path.size() > suffixFrro.size() && path.ends_with(suffixFrro))
+        || (path.size() > suffixIdmap.size() && path.ends_with(suffixIdmap));
 }
 
-bool IsFabricatedOverlay(const char* path) {
-  auto fd = base::unique_fd(base::utf8::open(path, O_RDONLY|O_CLOEXEC));
+bool IsFabricatedOverlay(std::string_view path) {
+  if (!IsFabricatedOverlayName(path)) {
+    return false;
+  }
+  std::string path_copy;
+  if (path[path.size()] != '\0') {
+    path_copy.assign(path);
+    path = path_copy;
+  }
+  auto fd = base::unique_fd(base::utf8::open(path.data(), O_RDONLY|O_CLOEXEC|O_BINARY));
   if (fd < 0) {
     return false;
   }
@@ -7319,9 +7333,6 @@
 public:
     void add(uint32_t targetResId, uint32_t overlayResId) {
         uint8_t targetTypeId = Res_GETTYPE(targetResId);
-        if (mData.find(targetTypeId) == mData.end()) {
-            mData.emplace(targetTypeId, std::set<std::pair<uint32_t, uint32_t>>());
-        }
         auto& entries = mData[targetTypeId];
         entries.insert(std::make_pair(targetResId, overlayResId));
     }
diff --git a/libs/androidfw/include/androidfw/Idmap.h b/libs/androidfw/include/androidfw/Idmap.h
index d9f7c2a..c32a38e 100644
--- a/libs/androidfw/include/androidfw/Idmap.h
+++ b/libs/androidfw/include/androidfw/Idmap.h
@@ -23,6 +23,7 @@
 #include <variant>
 
 #include "android-base/macros.h"
+#include "android-base/unique_fd.h"
 #include "androidfw/ConfigDescription.h"
 #include "androidfw/StringPiece.h"
 #include "androidfw/ResourceTypes.h"
@@ -159,11 +160,6 @@
   // Loads an IDMAP from a chunk of memory. Returns nullptr if the IDMAP data was malformed.
   static std::unique_ptr<LoadedIdmap> Load(StringPiece idmap_path, StringPiece idmap_data);
 
-  // Returns the path to the IDMAP.
-  std::string_view IdmapPath() const {
-    return idmap_path_;
-  }
-
   // Returns the path to the RRO (Runtime Resource Overlay) APK for which this IDMAP was generated.
   std::string_view OverlayApkPath() const {
     return overlay_apk_path_;
@@ -203,7 +199,7 @@
   const Idmap_overlay_entry* overlay_entries_;
   const std::unique_ptr<ResStringPool> string_pool_;
 
-  std::string idmap_path_;
+  android::base::unique_fd idmap_fd_;
   std::string_view overlay_apk_path_;
   std::string_view target_apk_path_;
   time_t idmap_last_mod_time_;
@@ -211,7 +207,7 @@
  private:
   DISALLOW_COPY_AND_ASSIGN(LoadedIdmap);
 
-  explicit LoadedIdmap(std::string&& idmap_path,
+  explicit LoadedIdmap(const std::string& idmap_path,
                        const Idmap_header* header,
                        const Idmap_data_header* data_header,
                        const Idmap_target_entry* target_entries,
diff --git a/libs/androidfw/include/androidfw/ResourceTypes.h b/libs/androidfw/include/androidfw/ResourceTypes.h
index 3d1403d..c264890 100644
--- a/libs/androidfw/include/androidfw/ResourceTypes.h
+++ b/libs/androidfw/include/androidfw/ResourceTypes.h
@@ -59,8 +59,8 @@
 constexpr const uint32_t kFabricatedOverlayCurrentVersion = 3;
 
 // Returns whether or not the path represents a fabricated overlay.
-bool IsFabricatedOverlay(const std::string& path);
-bool IsFabricatedOverlay(const char* path);
+bool IsFabricatedOverlayName(std::string_view path);
+bool IsFabricatedOverlay(std::string_view path);
 bool IsFabricatedOverlay(android::base::borrowed_fd fd);
 
 /**
diff --git a/libs/androidfw/include/androidfw/misc.h b/libs/androidfw/include/androidfw/misc.h
index d40d24e..077609d 100644
--- a/libs/androidfw/include/androidfw/misc.h
+++ b/libs/androidfw/include/androidfw/misc.h
@@ -43,6 +43,8 @@
 FileType getFileType(const char* fileName);
 /* get the file's modification date; returns -1 w/errno set on failure */
 time_t getFileModDate(const char* fileName);
+/* same, but also returns -1 if the file has already been deleted */
+time_t getFileModDate(int fd);
 
 // Check if |path| or |fd| resides on a readonly filesystem.
 bool isReadonlyFilesystem(const char* path);
diff --git a/libs/androidfw/misc.cpp b/libs/androidfw/misc.cpp
index d3949e9..93dcaf5 100644
--- a/libs/androidfw/misc.cpp
+++ b/libs/androidfw/misc.cpp
@@ -76,13 +76,23 @@
 /*
  * Get a file's modification date.
  */
-time_t getFileModDate(const char* fileName)
-{
+time_t getFileModDate(const char* fileName) {
     struct stat sb;
+    if (stat(fileName, &sb) < 0) {
+        return (time_t)-1;
+    }
+    return sb.st_mtime;
+}
 
-    if (stat(fileName, &sb) < 0)
-        return (time_t) -1;
-
+time_t getFileModDate(int fd) {
+    struct stat sb;
+    if (fstat(fd, &sb) < 0) {
+        return (time_t)-1;
+    }
+    if (sb.st_nlink <= 0) {
+        errno = ENOENT;
+        return (time_t)-1;
+    }
     return sb.st_mtime;
 }