diff --git a/BUILD b/BUILD
index d10c9fdb567..8c10f118c27 100644
--- a/BUILD
+++ b/BUILD
@@ -57,6 +57,7 @@ GPR_PUBLIC_HDRS = [
     "include/grpc/support/string_util.h",
     "include/grpc/support/subprocess.h",
     "include/grpc/support/sync.h",
+    "include/grpc/support/sync_custom.h",
     "include/grpc/support/sync_generic.h",
     "include/grpc/support/sync_posix.h",
     "include/grpc/support/sync_windows.h",
@@ -545,6 +546,7 @@ grpc_cc_library(
         "include/grpc/impl/codegen/gpr_types.h",
         "include/grpc/impl/codegen/port_platform.h",
         "include/grpc/impl/codegen/sync.h",
+        "include/grpc/impl/codegen/sync_custom.h",
         "include/grpc/impl/codegen/sync_generic.h",
         "include/grpc/impl/codegen/sync_posix.h",
         "include/grpc/impl/codegen/sync_windows.h",
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0b593a9ae5c..8b869e09c2d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -867,6 +867,7 @@ foreach(_hdr
   include/grpc/support/string_util.h
   include/grpc/support/subprocess.h
   include/grpc/support/sync.h
+  include/grpc/support/sync_custom.h
   include/grpc/support/sync_generic.h
   include/grpc/support/sync_posix.h
   include/grpc/support/sync_windows.h
@@ -885,6 +886,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -1260,6 +1262,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -1566,6 +1569,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -1842,6 +1846,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -2102,6 +2107,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -2397,6 +2403,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -2661,6 +2668,7 @@ foreach(_hdr
   include/grpc/support/string_util.h
   include/grpc/support/subprocess.h
   include/grpc/support/sync.h
+  include/grpc/support/sync_custom.h
   include/grpc/support/sync_generic.h
   include/grpc/support/sync_posix.h
   include/grpc/support/sync_windows.h
@@ -2679,6 +2687,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -3092,6 +3101,7 @@ foreach(_hdr
   include/grpc/support/string_util.h
   include/grpc/support/subprocess.h
   include/grpc/support/sync.h
+  include/grpc/support/sync_custom.h
   include/grpc/support/sync_generic.h
   include/grpc/support/sync_posix.h
   include/grpc/support/sync_windows.h
@@ -3110,6 +3120,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -3547,6 +3558,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -3686,6 +3698,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
@@ -3839,6 +3852,7 @@ foreach(_hdr
   include/grpc/support/string_util.h
   include/grpc/support/subprocess.h
   include/grpc/support/sync.h
+  include/grpc/support/sync_custom.h
   include/grpc/support/sync_generic.h
   include/grpc/support/sync_posix.h
   include/grpc/support/sync_windows.h
@@ -3857,6 +3871,7 @@ foreach(_hdr
   include/grpc/impl/codegen/gpr_types.h
   include/grpc/impl/codegen/port_platform.h
   include/grpc/impl/codegen/sync.h
+  include/grpc/impl/codegen/sync_custom.h
   include/grpc/impl/codegen/sync_generic.h
   include/grpc/impl/codegen/sync_posix.h
   include/grpc/impl/codegen/sync_windows.h
diff --git a/Makefile b/Makefile
index 392c8f318fc..fb7bca5de81 100644
--- a/Makefile
+++ b/Makefile
@@ -2809,6 +2809,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/support/string_util.h \
     include/grpc/support/subprocess.h \
     include/grpc/support/sync.h \
+    include/grpc/support/sync_custom.h \
     include/grpc/support/sync_generic.h \
     include/grpc/support/sync_posix.h \
     include/grpc/support/sync_windows.h \
@@ -2827,6 +2828,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -3170,6 +3172,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -3474,6 +3477,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -3749,6 +3753,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -3998,6 +4003,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -4268,6 +4274,7 @@ PUBLIC_HEADERS_C += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -4505,6 +4512,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/support/string_util.h \
     include/grpc/support/subprocess.h \
     include/grpc/support/sync.h \
+    include/grpc/support/sync_custom.h \
     include/grpc/support/sync_generic.h \
     include/grpc/support/sync_posix.h \
     include/grpc/support/sync_windows.h \
@@ -4523,6 +4531,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -4943,6 +4952,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/support/string_util.h \
     include/grpc/support/subprocess.h \
     include/grpc/support/sync.h \
+    include/grpc/support/sync_custom.h \
     include/grpc/support/sync_generic.h \
     include/grpc/support/sync_posix.h \
     include/grpc/support/sync_windows.h \
@@ -4961,6 +4971,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -5381,6 +5392,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -5495,6 +5507,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
@@ -5651,6 +5664,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/support/string_util.h \
     include/grpc/support/subprocess.h \
     include/grpc/support/sync.h \
+    include/grpc/support/sync_custom.h \
     include/grpc/support/sync_generic.h \
     include/grpc/support/sync_posix.h \
     include/grpc/support/sync_windows.h \
@@ -5669,6 +5683,7 @@ PUBLIC_HEADERS_CXX += \
     include/grpc/impl/codegen/gpr_types.h \
     include/grpc/impl/codegen/port_platform.h \
     include/grpc/impl/codegen/sync.h \
+    include/grpc/impl/codegen/sync_custom.h \
     include/grpc/impl/codegen/sync_generic.h \
     include/grpc/impl/codegen/sync_posix.h \
     include/grpc/impl/codegen/sync_windows.h \
diff --git a/build.yaml b/build.yaml
index 2e55837fcc7..32ce5e949cc 100644
--- a/build.yaml
+++ b/build.yaml
@@ -126,6 +126,7 @@ filegroups:
   - include/grpc/support/string_util.h
   - include/grpc/support/subprocess.h
   - include/grpc/support/sync.h
+  - include/grpc/support/sync_custom.h
   - include/grpc/support/sync_generic.h
   - include/grpc/support/sync_posix.h
   - include/grpc/support/sync_windows.h
@@ -166,6 +167,7 @@ filegroups:
   - include/grpc/impl/codegen/gpr_types.h
   - include/grpc/impl/codegen/port_platform.h
   - include/grpc/impl/codegen/sync.h
+  - include/grpc/impl/codegen/sync_custom.h
   - include/grpc/impl/codegen/sync_generic.h
   - include/grpc/impl/codegen/sync_posix.h
   - include/grpc/impl/codegen/sync_windows.h
diff --git a/gRPC-Core.podspec b/gRPC-Core.podspec
index 1d865453521..74fa6046ca0 100644
--- a/gRPC-Core.podspec
+++ b/gRPC-Core.podspec
@@ -118,6 +118,7 @@ Pod::Spec.new do |s|
                       'include/grpc/support/string_util.h',
                       'include/grpc/support/subprocess.h',
                       'include/grpc/support/sync.h',
+                      'include/grpc/support/sync_custom.h',
                       'include/grpc/support/sync_generic.h',
                       'include/grpc/support/sync_posix.h',
                       'include/grpc/support/sync_windows.h',
@@ -136,6 +137,7 @@ Pod::Spec.new do |s|
                       'include/grpc/impl/codegen/gpr_types.h',
                       'include/grpc/impl/codegen/port_platform.h',
                       'include/grpc/impl/codegen/sync.h',
+                      'include/grpc/impl/codegen/sync_custom.h',
                       'include/grpc/impl/codegen/sync_generic.h',
                       'include/grpc/impl/codegen/sync_posix.h',
                       'include/grpc/impl/codegen/sync_windows.h',
@@ -155,6 +157,7 @@ Pod::Spec.new do |s|
                       'include/grpc/impl/codegen/gpr_types.h',
                       'include/grpc/impl/codegen/port_platform.h',
                       'include/grpc/impl/codegen/sync.h',
+                      'include/grpc/impl/codegen/sync_custom.h',
                       'include/grpc/impl/codegen/sync_generic.h',
                       'include/grpc/impl/codegen/sync_posix.h',
                       'include/grpc/impl/codegen/sync_windows.h',
diff --git a/grpc.gemspec b/grpc.gemspec
index 6e3d410b694..76280c5a939 100644
--- a/grpc.gemspec
+++ b/grpc.gemspec
@@ -59,6 +59,7 @@ Gem::Specification.new do |s|
   s.files += %w( include/grpc/support/string_util.h )
   s.files += %w( include/grpc/support/subprocess.h )
   s.files += %w( include/grpc/support/sync.h )
+  s.files += %w( include/grpc/support/sync_custom.h )
   s.files += %w( include/grpc/support/sync_generic.h )
   s.files += %w( include/grpc/support/sync_posix.h )
   s.files += %w( include/grpc/support/sync_windows.h )
@@ -77,6 +78,7 @@ Gem::Specification.new do |s|
   s.files += %w( include/grpc/impl/codegen/gpr_types.h )
   s.files += %w( include/grpc/impl/codegen/port_platform.h )
   s.files += %w( include/grpc/impl/codegen/sync.h )
+  s.files += %w( include/grpc/impl/codegen/sync_custom.h )
   s.files += %w( include/grpc/impl/codegen/sync_generic.h )
   s.files += %w( include/grpc/impl/codegen/sync_posix.h )
   s.files += %w( include/grpc/impl/codegen/sync_windows.h )
@@ -159,6 +161,7 @@ Gem::Specification.new do |s|
   s.files += %w( include/grpc/impl/codegen/gpr_types.h )
   s.files += %w( include/grpc/impl/codegen/port_platform.h )
   s.files += %w( include/grpc/impl/codegen/sync.h )
+  s.files += %w( include/grpc/impl/codegen/sync_custom.h )
   s.files += %w( include/grpc/impl/codegen/sync_generic.h )
   s.files += %w( include/grpc/impl/codegen/sync_posix.h )
   s.files += %w( include/grpc/impl/codegen/sync_windows.h )
diff --git a/include/grpc/impl/codegen/sync.h b/include/grpc/impl/codegen/sync.h
index de4e99be63b..6cdb0c5153d 100644
--- a/include/grpc/impl/codegen/sync.h
+++ b/include/grpc/impl/codegen/sync.h
@@ -49,7 +49,9 @@ extern "C" {
 #include <grpc/impl/codegen/sync_posix.h>
 #elif defined(GPR_WINDOWS)
 #include <grpc/impl/codegen/sync_windows.h>
-#elif !defined(GPR_CUSTOM_SYNC)
+#elif defined(GPR_CUSTOM_SYNC)
+#include <grpc/impl/codegen/sync_custom.h>
+#else
 #error Unable to determine platform for sync
 #endif
 
diff --git a/include/grpc/impl/codegen/sync_custom.h b/include/grpc/impl/codegen/sync_custom.h
new file mode 100644
index 00000000000..f7f7d121d82
--- /dev/null
+++ b/include/grpc/impl/codegen/sync_custom.h
@@ -0,0 +1,32 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_IMPL_CODEGEN_SYNC_CUSTOM_H
+#define GRPC_IMPL_CODEGEN_SYNC_CUSTOM_H
+
+#include <grpc/impl/codegen/sync_generic.h>
+
+/* Users defining GPR_CUSTOM_SYNC need to define the following macros. */
+
+typedef GPR_CUSTOM_MU_TYPE gpr_mu;
+typedef GPR_CUSTOM_CV_TYPE gpr_cv;
+typedef GPR_CUSTOM_ONCE_TYPE gpr_once;
+
+#define GPR_ONCE_INIT GPR_CUSTOM_ONCE_INIT
+
+#endif /* GRPC_IMPL_CODEGEN_SYNC_CUSTOM_H */
diff --git a/include/grpc/support/sync_custom.h b/include/grpc/support/sync_custom.h
new file mode 100644
index 00000000000..b575f5e0028
--- /dev/null
+++ b/include/grpc/support/sync_custom.h
@@ -0,0 +1,24 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_SUPPORT_SYNC_CUSTOM_H
+#define GRPC_SUPPORT_SYNC_CUSTOM_H
+
+#include <grpc/impl/codegen/sync_custom.h>
+
+#endif /* GRPC_SUPPORT_SYNC_CUSTOM_H */
diff --git a/package.xml b/package.xml
index 195447e23c1..0a9d4868119 100644
--- a/package.xml
+++ b/package.xml
@@ -69,6 +69,7 @@
     <file baseinstalldir="/" name="include/grpc/support/string_util.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/support/subprocess.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/support/sync.h" role="src" />
+    <file baseinstalldir="/" name="include/grpc/support/sync_custom.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/support/sync_generic.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/support/sync_posix.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/support/sync_windows.h" role="src" />
@@ -87,6 +88,7 @@
     <file baseinstalldir="/" name="include/grpc/impl/codegen/gpr_types.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/port_platform.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync.h" role="src" />
+    <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_custom.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_generic.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_posix.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_windows.h" role="src" />
@@ -169,6 +171,7 @@
     <file baseinstalldir="/" name="include/grpc/impl/codegen/gpr_types.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/port_platform.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync.h" role="src" />
+    <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_custom.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_generic.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_posix.h" role="src" />
     <file baseinstalldir="/" name="include/grpc/impl/codegen/sync_windows.h" role="src" />
diff --git a/test/core/surface/public_headers_must_be_c89.c b/test/core/surface/public_headers_must_be_c89.c
index 3b1c53390b3..0d7f68c0add 100644
--- a/test/core/surface/public_headers_must_be_c89.c
+++ b/test/core/surface/public_headers_must_be_c89.c
@@ -36,6 +36,7 @@
 #include <grpc/impl/codegen/slice.h>
 #include <grpc/impl/codegen/status.h>
 #include <grpc/impl/codegen/sync.h>
+#include <grpc/impl/codegen/sync_custom.h>
 #include <grpc/impl/codegen/sync_generic.h>
 #include <grpc/load_reporting.h>
 #include <grpc/slice.h>
@@ -53,6 +54,7 @@
 #include <grpc/support/string_util.h>
 #include <grpc/support/subprocess.h>
 #include <grpc/support/sync.h>
+#include <grpc/support/sync_custom.h>
 #include <grpc/support/sync_generic.h>
 #include <grpc/support/thd.h>
 #include <grpc/support/time.h>
diff --git a/tools/doxygen/Doxyfile.c++ b/tools/doxygen/Doxyfile.c++
index b83e581e06a..62f113907db 100644
--- a/tools/doxygen/Doxyfile.c++
+++ b/tools/doxygen/Doxyfile.c++
@@ -893,6 +893,7 @@ include/grpc/impl/codegen/propagation_bits.h \
 include/grpc/impl/codegen/slice.h \
 include/grpc/impl/codegen/status.h \
 include/grpc/impl/codegen/sync.h \
+include/grpc/impl/codegen/sync_custom.h \
 include/grpc/impl/codegen/sync_generic.h \
 include/grpc/impl/codegen/sync_posix.h \
 include/grpc/impl/codegen/sync_windows.h \
@@ -916,6 +917,7 @@ include/grpc/support/port_platform.h \
 include/grpc/support/string_util.h \
 include/grpc/support/subprocess.h \
 include/grpc/support/sync.h \
+include/grpc/support/sync_custom.h \
 include/grpc/support/sync_generic.h \
 include/grpc/support/sync_posix.h \
 include/grpc/support/sync_windows.h \
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index 4389aebb97a..6e80ab2443e 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -894,6 +894,7 @@ include/grpc/impl/codegen/propagation_bits.h \
 include/grpc/impl/codegen/slice.h \
 include/grpc/impl/codegen/status.h \
 include/grpc/impl/codegen/sync.h \
+include/grpc/impl/codegen/sync_custom.h \
 include/grpc/impl/codegen/sync_generic.h \
 include/grpc/impl/codegen/sync_posix.h \
 include/grpc/impl/codegen/sync_windows.h \
@@ -917,6 +918,7 @@ include/grpc/support/port_platform.h \
 include/grpc/support/string_util.h \
 include/grpc/support/subprocess.h \
 include/grpc/support/sync.h \
+include/grpc/support/sync_custom.h \
 include/grpc/support/sync_generic.h \
 include/grpc/support/sync_posix.h \
 include/grpc/support/sync_windows.h \
diff --git a/tools/doxygen/Doxyfile.core b/tools/doxygen/Doxyfile.core
index c5ae421d40c..e4cc1c7461d 100644
--- a/tools/doxygen/Doxyfile.core
+++ b/tools/doxygen/Doxyfile.core
@@ -827,6 +827,8 @@ include/grpc/impl/codegen/slice.h \
 include/grpc/impl/codegen/status.h \
 include/grpc/impl/codegen/sync.h \
 include/grpc/impl/codegen/sync.h \
+include/grpc/impl/codegen/sync_custom.h \
+include/grpc/impl/codegen/sync_custom.h \
 include/grpc/impl/codegen/sync_generic.h \
 include/grpc/impl/codegen/sync_generic.h \
 include/grpc/impl/codegen/sync_posix.h \
@@ -853,6 +855,7 @@ include/grpc/support/port_platform.h \
 include/grpc/support/string_util.h \
 include/grpc/support/subprocess.h \
 include/grpc/support/sync.h \
+include/grpc/support/sync_custom.h \
 include/grpc/support/sync_generic.h \
 include/grpc/support/sync_posix.h \
 include/grpc/support/sync_windows.h \
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index f678b70b67e..8a1d77c3e74 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -827,6 +827,8 @@ include/grpc/impl/codegen/slice.h \
 include/grpc/impl/codegen/status.h \
 include/grpc/impl/codegen/sync.h \
 include/grpc/impl/codegen/sync.h \
+include/grpc/impl/codegen/sync_custom.h \
+include/grpc/impl/codegen/sync_custom.h \
 include/grpc/impl/codegen/sync_generic.h \
 include/grpc/impl/codegen/sync_generic.h \
 include/grpc/impl/codegen/sync_posix.h \
@@ -853,6 +855,7 @@ include/grpc/support/port_platform.h \
 include/grpc/support/string_util.h \
 include/grpc/support/subprocess.h \
 include/grpc/support/sync.h \
+include/grpc/support/sync_custom.h \
 include/grpc/support/sync_generic.h \
 include/grpc/support/sync_posix.h \
 include/grpc/support/sync_windows.h \
diff --git a/tools/run_tests/generated/sources_and_headers.json b/tools/run_tests/generated/sources_and_headers.json
index 12e4390f5cb..df8ad292d2d 100644
--- a/tools/run_tests/generated/sources_and_headers.json
+++ b/tools/run_tests/generated/sources_and_headers.json
@@ -7646,6 +7646,7 @@
       "include/grpc/support/string_util.h", 
       "include/grpc/support/subprocess.h", 
       "include/grpc/support/sync.h", 
+      "include/grpc/support/sync_custom.h", 
       "include/grpc/support/sync_generic.h", 
       "include/grpc/support/sync_posix.h", 
       "include/grpc/support/sync_windows.h", 
@@ -7694,6 +7695,7 @@
       "include/grpc/support/string_util.h", 
       "include/grpc/support/subprocess.h", 
       "include/grpc/support/sync.h", 
+      "include/grpc/support/sync_custom.h", 
       "include/grpc/support/sync_generic.h", 
       "include/grpc/support/sync_posix.h", 
       "include/grpc/support/sync_windows.h", 
@@ -7736,6 +7738,7 @@
       "include/grpc/impl/codegen/gpr_types.h", 
       "include/grpc/impl/codegen/port_platform.h", 
       "include/grpc/impl/codegen/sync.h", 
+      "include/grpc/impl/codegen/sync_custom.h", 
       "include/grpc/impl/codegen/sync_generic.h", 
       "include/grpc/impl/codegen/sync_posix.h", 
       "include/grpc/impl/codegen/sync_windows.h"
@@ -7752,6 +7755,7 @@
       "include/grpc/impl/codegen/gpr_types.h", 
       "include/grpc/impl/codegen/port_platform.h", 
       "include/grpc/impl/codegen/sync.h", 
+      "include/grpc/impl/codegen/sync_custom.h", 
       "include/grpc/impl/codegen/sync_generic.h", 
       "include/grpc/impl/codegen/sync_posix.h", 
       "include/grpc/impl/codegen/sync_windows.h"