diff --git a/HISTORY.rst b/HISTORY.rst
index 90089cb4..c4371ce5 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -11,6 +11,7 @@ PlatformIO Core 5
 5.2.1 (2021-??-??)
 ~~~~~~~~~~~~~~~~~~
 
+- Allowed to override a default library builder via a new ``builder`` field in a ``build`` group of `library.json <https://docs.platformio.org/page/librarymanager/config.html#build>`__ manifest (`issue #3957 <https://github.com/platformio/platformio-core/issues/3957>`_)
 - Fixed a "KeyError: Invalid board option 'build.cpu'" when using a precompiled library with a board that does not have a CPU field in the manifest (`issue #4056 <https://github.com/platformio/platformio-core/issues/4056>`_)
 - Fixed a "FileExist" error when the `platformio ci <https://docs.platformio.org/en/latest/userguide/cmd_ci.html>`__ command is used in pair with the ``--keep-build-dir`` option (`issue #4011 <https://github.com/platformio/platformio-core/issues/4011>`_)
 
diff --git a/docs b/docs
index 395b056f..c9c5b9cd 160000
--- a/docs
+++ b/docs
@@ -1 +1 @@
-Subproject commit 395b056f8e6ee5cbb7e622465622e7b08431868f
+Subproject commit c9c5b9cd5f18b17be71225df1bf5b487660e58e1
diff --git a/platformio/builder/tools/piolib.py b/platformio/builder/tools/piolib.py
index 902cf653..9b6d9642 100644
--- a/platformio/builder/tools/piolib.py
+++ b/platformio/builder/tools/piolib.py
@@ -59,6 +59,16 @@ class LibBuilderFactory(object):
                 clsname = "%sLibBuilder" % used_frameworks[0].title()
 
         obj = getattr(sys.modules[__name__], clsname)(env, path, verbose=verbose)
+
+        # Handle PlatformIOLibBuilder.manifest.build.builder
+        # pylint: disable=protected-access
+        if isinstance(obj, PlatformIOLibBuilder) and obj._manifest.get("build", {}).get(
+            "builder"
+        ):
+            obj = getattr(
+                sys.modules[__name__], obj._manifest.get("build", {}).get("builder")
+            )(env, path, verbose=verbose)
+
         assert isinstance(obj, LibBuilderBase)
         return obj