diff --git a/build/cmake/android-legacy.toolchain.cmake b/build/cmake/android-legacy.toolchain.cmake
index 9d9ae353..3a0dd713 100644
--- a/build/cmake/android-legacy.toolchain.cmake
+++ b/build/cmake/android-legacy.toolchain.cmake
@@ -457,6 +457,7 @@ list(APPEND ANDROID_LINKER_FLAGS -Wl,--gc-sections)
 list(APPEND ANDROID_LINKER_FLAGS_EXE -Wl,--gc-sections)
 
 # Debug and release flags.
+list(APPEND ANDROID_COMPILER_FLAGS_RELEASE -O3)
 list(APPEND ANDROID_COMPILER_FLAGS_RELEASE -DNDEBUG)
 if(ANDROID_TOOLCHAIN STREQUAL clang)
   list(APPEND ANDROID_COMPILER_FLAGS_DEBUG -fno-limit-debug-info)
diff --git a/docs/changelogs/Changelog-r25.md b/docs/changelogs/Changelog-r25.md
index 0c4cf0ac..78a34650 100644
--- a/docs/changelogs/Changelog-r25.md
+++ b/docs/changelogs/Changelog-r25.md
@@ -11,6 +11,17 @@ directly, see the [build system maintainers guide].
 [Android Studio site]: http://tools.android.com/filing-bugs
 [build system maintainers guide]: https://android.googlesource.com/platform/ndk/+/master/docs/BuildSystemMaintainers.md
 
+
+## r25b
+
+* [Issue 1740]: Fixed the legacy toolchain when using CMake's `Release` build
+  configuration. Since r23b it has not be receiving any optimization flag. It
+  will now receive `-O3`. If you're building with AGP and haven't overridden
+  AGP's default CMake modes, this change does not affect you, as AGP uses
+  `RelWithDebInfo` by default.
+
+[Issue 1740]: https://github.com/android/ndk/issues/1740
+
 ## Changes
 
 * Includes Android 13 Beta 2 APIs.
diff --git a/tests/build/cmake_default_flags/test.py b/tests/build/cmake_default_flags/test.py
index a7ead75a..ca367a29 100644
--- a/tests/build/cmake_default_flags/test.py
+++ b/tests/build/cmake_default_flags/test.py
@@ -18,17 +18,38 @@
 from typing import Optional
 
 from ndk.test.spec import BuildConfiguration
-from ndk.testing.flag_verifier import FlagVerifier
+from ndk.testing.flag_verifier import FlagVerifier, FlagVerifierResult
 
 
-def run_test(ndk_path: str,
-             config: BuildConfiguration) -> tuple[bool, Optional[str]]:
-    """Check that the CMake toolchain uses the correct default flags.
+def check_configuration(
+    ndk_path: str,
+    build_config: BuildConfiguration,
+    cmake_config: str,
+    expected_flags: list[str],
+    unexpected_flags: list[str],
+) -> FlagVerifierResult:
+    verifier = FlagVerifier(Path("project"), Path(ndk_path), build_config)
+    for flag in expected_flags:
+        verifier.expect_flag(flag)
+    for flag in unexpected_flags:
+        verifier.expect_not_flag(flag)
+    return verifier.verify_cmake([f"-DCMAKE_BUILD_TYPE={cmake_config}"])
 
-    Currently this only tests the optimization flags for RelWithDebInfo, but
-    it's probably worth expanding in the future.
-    """
-    verifier = FlagVerifier(Path('project'), Path(ndk_path), config)
-    verifier.expect_flag('-O2')
-    return verifier.verify_cmake(['-DCMAKE_BUILD_TYPE=RelWithDebInfo'
-                                  ]).make_test_result_tuple()
+
+def run_test(ndk_path: str, config: BuildConfiguration) -> tuple[bool, Optional[str]]:
+    """Check that the CMake toolchain uses the correct default flags."""
+    verify_configs: dict[str, tuple[list[str], list[str]]] = {
+        # No flag is the same as -O0. As long as no other opt flag is used, the default
+        # is fine.
+        "Debug": ([], ["-O1", "-O2", "-O3", "-Os", "-Oz"]),
+        "MinSizeRel": (["-Os"], ["-O0", "-O1", "-O2", "-O3", "-Oz"]),
+        "Release": (["-O3"], ["-O0", "-O1", "-O2", "-Os", "-Oz"]),
+        "RelWithDebInfo": (["-O2"], ["-O0", "-O1", "-O3", "-Os", "-Oz"]),
+    }
+    for cmake_config, (expected_flags, unexpected_flags) in verify_configs.items():
+        result = check_configuration(
+            ndk_path, config, cmake_config, expected_flags, unexpected_flags
+        )
+        if result.failed():
+            return result.make_test_result_tuple()
+    return result.make_test_result_tuple()