diff --git a/templates/tools/doxygen/Doxyfile.include b/templates/tools/doxygen/Doxyfile.include
index e26ae2b948a..56e6c0b0552 100644
--- a/templates/tools/doxygen/Doxyfile.include
+++ b/templates/tools/doxygen/Doxyfile.include
@@ -787,7 +787,7 @@ WARN_LOGFILE           =
 # Note: If this tag is empty the current directory is searched.
 
 INPUT                  = ${
-    ' \\\n'.join(sorted(
+    ' \\\n'.join(sorted(set(
         itertools.chain(
             itertools.chain.from_iterable(
     			      target.public_headers +
@@ -798,7 +798,7 @@ INPUT                  = ${
             glob.glob('doc/*.md'),
             glob.glob('doc/%s/*.md' % docpackage),
             [] if not internal else srcdoc)
-    ))
+    )))
 }
 
 # This tag can be used to specify the character encoding of the source files
diff --git a/templates/tools/doxygen/Doxyfile.objc.include b/templates/tools/doxygen/Doxyfile.objc.include
index 5e5867f0417..fb87d23ce1e 100644
--- a/templates/tools/doxygen/Doxyfile.objc.include
+++ b/templates/tools/doxygen/Doxyfile.objc.include
@@ -784,13 +784,13 @@ WARN_LOGFILE           =
 # Note: If this tag is empty the current directory is searched.
 
 INPUT                  = ${
-    ' \\\n'.join(sorted(
+    ' \\\n'.join(sorted(set(
         itertools.chain(
             glob.glob('src/objective-c/GRPCClient/*.h') if not internal else glob_recursive('src/objective-c/GRPCClient', '*.h'),
             glob.glob('src/objective-c/ProtoRPC/*.h'),
             glob.glob('src/objective-c/RxLibrary/*.h') if not internal else glob_recursive('src/objective-c/RxLibrary', '*.h'),
             glob.glob('doc/*.md'),
-            srcdoc)))
+            srcdoc))))
 }
 
 # This tag can be used to specify the character encoding of the source files
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index 46d038eac5d..d1da5829623 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -826,7 +826,6 @@ include/grpc++/impl/codegen/completion_queue_tag.h \
 include/grpc++/impl/codegen/config.h \
 include/grpc++/impl/codegen/config_protobuf.h \
 include/grpc++/impl/codegen/core_codegen.h \
-include/grpc++/impl/codegen/core_codegen.h \
 include/grpc++/impl/codegen/core_codegen_interface.h \
 include/grpc++/impl/codegen/create_auth_context.h \
 include/grpc++/impl/codegen/grpc_library.h \
@@ -975,7 +974,6 @@ include/grpcpp/impl/codegen/completion_queue_tag.h \
 include/grpcpp/impl/codegen/config.h \
 include/grpcpp/impl/codegen/config_protobuf.h \
 include/grpcpp/impl/codegen/core_codegen.h \
-include/grpcpp/impl/codegen/core_codegen.h \
 include/grpcpp/impl/codegen/core_codegen_interface.h \
 include/grpcpp/impl/codegen/create_auth_context.h \
 include/grpcpp/impl/codegen/delegating_channel.h \
diff --git a/tools/doxygen/Doxyfile.core b/tools/doxygen/Doxyfile.core
index 0c0e95a1920..9ab5b3e429c 100644
--- a/tools/doxygen/Doxyfile.core
+++ b/tools/doxygen/Doxyfile.core
@@ -816,43 +816,28 @@ include/grpc/grpc_posix.h \
 include/grpc/grpc_security.h \
 include/grpc/grpc_security_constants.h \
 include/grpc/impl/codegen/atm.h \
-include/grpc/impl/codegen/atm.h \
-include/grpc/impl/codegen/atm_gcc_atomic.h \
 include/grpc/impl/codegen/atm_gcc_atomic.h \
 include/grpc/impl/codegen/atm_gcc_sync.h \
-include/grpc/impl/codegen/atm_gcc_sync.h \
-include/grpc/impl/codegen/atm_windows.h \
 include/grpc/impl/codegen/atm_windows.h \
 include/grpc/impl/codegen/byte_buffer.h \
 include/grpc/impl/codegen/byte_buffer_reader.h \
 include/grpc/impl/codegen/compression_types.h \
 include/grpc/impl/codegen/connectivity_state.h \
 include/grpc/impl/codegen/fork.h \
-include/grpc/impl/codegen/fork.h \
-include/grpc/impl/codegen/gpr_slice.h \
 include/grpc/impl/codegen/gpr_slice.h \
 include/grpc/impl/codegen/gpr_types.h \
-include/grpc/impl/codegen/gpr_types.h \
 include/grpc/impl/codegen/grpc_types.h \
 include/grpc/impl/codegen/log.h \
-include/grpc/impl/codegen/log.h \
-include/grpc/impl/codegen/port_platform.h \
 include/grpc/impl/codegen/port_platform.h \
 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.h \
 include/grpc/impl/codegen/sync_abseil.h \
-include/grpc/impl/codegen/sync_abseil.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 \
 include/grpc/impl/codegen/sync_posix.h \
 include/grpc/impl/codegen/sync_windows.h \
-include/grpc/impl/codegen/sync_windows.h \
 include/grpc/load_reporting.h \
 include/grpc/slice.h \
 include/grpc/slice_buffer.h \
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index 8318caf4f27..04cb62c32bc 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -816,43 +816,28 @@ include/grpc/grpc_posix.h \
 include/grpc/grpc_security.h \
 include/grpc/grpc_security_constants.h \
 include/grpc/impl/codegen/atm.h \
-include/grpc/impl/codegen/atm.h \
-include/grpc/impl/codegen/atm_gcc_atomic.h \
 include/grpc/impl/codegen/atm_gcc_atomic.h \
 include/grpc/impl/codegen/atm_gcc_sync.h \
-include/grpc/impl/codegen/atm_gcc_sync.h \
-include/grpc/impl/codegen/atm_windows.h \
 include/grpc/impl/codegen/atm_windows.h \
 include/grpc/impl/codegen/byte_buffer.h \
 include/grpc/impl/codegen/byte_buffer_reader.h \
 include/grpc/impl/codegen/compression_types.h \
 include/grpc/impl/codegen/connectivity_state.h \
 include/grpc/impl/codegen/fork.h \
-include/grpc/impl/codegen/fork.h \
-include/grpc/impl/codegen/gpr_slice.h \
 include/grpc/impl/codegen/gpr_slice.h \
 include/grpc/impl/codegen/gpr_types.h \
-include/grpc/impl/codegen/gpr_types.h \
 include/grpc/impl/codegen/grpc_types.h \
 include/grpc/impl/codegen/log.h \
-include/grpc/impl/codegen/log.h \
-include/grpc/impl/codegen/port_platform.h \
 include/grpc/impl/codegen/port_platform.h \
 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.h \
 include/grpc/impl/codegen/sync_abseil.h \
-include/grpc/impl/codegen/sync_abseil.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 \
 include/grpc/impl/codegen/sync_posix.h \
 include/grpc/impl/codegen/sync_windows.h \
-include/grpc/impl/codegen/sync_windows.h \
 include/grpc/load_reporting.h \
 include/grpc/slice.h \
 include/grpc/slice_buffer.h \