diff --git a/CMakeLists.txt b/CMakeLists.txt
index ad1f5d2019a..83335cd674d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -373,7 +373,7 @@ if(NOT "${_repo_dir_name}" STREQUAL "executorch")
       "fix for this restriction."
   )
 endif()
-set(_common_include_directories ${CMAKE_CURRENT_SOURCE_DIR}/.. ${CMAKE_CURRENT_SOURCE_DIR}/runtime/core/portable_type)
+set(_common_include_directories ${CMAKE_CURRENT_SOURCE_DIR}/.. ${CMAKE_CURRENT_SOURCE_DIR}/runtime/core/portable_type/c10)
 
 #
 # The `_<target>_srcs` lists are defined by including ${EXECUTORCH_SRCS_FILE}.
diff --git a/backends/apple/coreml/CMakeLists.txt b/backends/apple/coreml/CMakeLists.txt
index 70daed7d065..01fe9d0f59a 100644
--- a/backends/apple/coreml/CMakeLists.txt
+++ b/backends/apple/coreml/CMakeLists.txt
@@ -134,7 +134,7 @@ target_include_directories(
   coremldelegate PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/runtime/util
 )
 target_include_directories(coremldelegate PRIVATE ${EXECUTORCH_ROOT}/..)
-target_include_directories(coremldelegate PRIVATE ${EXECUTORCH_ROOT}/runtime/core/portable_type)
+target_include_directories(coremldelegate PRIVATE ${EXECUTORCH_ROOT}/runtime/core/portable_type/c10)
 target_compile_definitions(coremldelegate PRIVATE C10_USING_CUSTOM_GENERATED_MACROS)
 target_link_libraries(coremldelegate PRIVATE executorch_core)
 
diff --git a/backends/apple/coreml/runtime/workspace/executorchcoreml.xcodeproj/project.pbxproj b/backends/apple/coreml/runtime/workspace/executorchcoreml.xcodeproj/project.pbxproj
index 2115f5a4806..198faebb9d7 100644
--- a/backends/apple/coreml/runtime/workspace/executorchcoreml.xcodeproj/project.pbxproj
+++ b/backends/apple/coreml/runtime/workspace/executorchcoreml.xcodeproj/project.pbxproj
@@ -922,7 +922,7 @@
 					"$(SRCROOT)/../kvstore",
 					"$(SRCROOT)/../inmemoryfs",
 					"$(SRCROOT)/../include",
-					"$(SRCROOT)/../include/executorch/runtime/core/portable_type",
+					"$(SRCROOT)/../include/executorch/runtime/core/portable_type/c10",
 					"$(SRCROOT)/../sdk",
 					"$(SRCROOT)/../util",
 					"$(SRCROOT)/../../third-party/nlohmann_json/single_include",
@@ -954,7 +954,7 @@
 					"$(SRCROOT)/../kvstore",
 					"$(SRCROOT)/../inmemoryfs",
 					"$(SRCROOT)/../include",
-					"$(SRCROOT)/../include/executorch/runtime/core/portable_type",
+					"$(SRCROOT)/../include/executorch/runtime/core/portable_type/c10",
 					"$(SRCROOT)/../sdk",
 					"$(SRCROOT)/../util",
 					"$(SRCROOT)/../../third-party/nlohmann_json/single_include",
diff --git a/backends/arm/CMakeLists.txt b/backends/arm/CMakeLists.txt
index 58d0389ea71..d91d3051a55 100644
--- a/backends/arm/CMakeLists.txt
+++ b/backends/arm/CMakeLists.txt
@@ -14,7 +14,7 @@ endif()
 
 include(${EXECUTORCH_ROOT}/build/Utils.cmake)
 
-set(_common_include_directories ${EXECUTORCH_ROOT}/.. ${EXECUTORCH_ROOT}/runtime/core/portable_type)
+set(_common_include_directories ${EXECUTORCH_ROOT}/.. ${EXECUTORCH_ROOT}/runtime/core/portable_type/c10)
 add_compile_definitions(C10_USING_CUSTOM_GENERATED_MACROS)
 
 # Third-party folder and Ethos-U driver inclued
diff --git a/backends/qualcomm/CMakeLists.txt b/backends/qualcomm/CMakeLists.txt
index 81d61fb0659..aefa929ee9f 100644
--- a/backends/qualcomm/CMakeLists.txt
+++ b/backends/qualcomm/CMakeLists.txt
@@ -74,7 +74,7 @@ endif()
 include_directories(
   BEFORE ${_common_include_directories} ${QNN_SDK_ROOT}/include/QNN
   ${EXECUTORCH_SOURCE_DIR}/third-party/flatbuffers/include
-  ${EXECUTORCH_SOURCE_DIR}/runtime/core/portable_type
+  ${EXECUTORCH_SOURCE_DIR}/runtime/core/portable_type/c10
 )
 
 set(_qnn_schema__srcs
diff --git a/build/build_apple_frameworks.sh b/build/build_apple_frameworks.sh
index 7ebfe2d9492..4d793ace0ab 100755
--- a/build/build_apple_frameworks.sh
+++ b/build/build_apple_frameworks.sh
@@ -207,11 +207,11 @@ check_command "$BUCK2"
 # So, just patch our generated framework to do that.
 sed -i '' '1i\
 #define C10_USING_CUSTOM_GENERATED_MACROS
-' $HEADERS_PATH/executorch/runtime/core/portable_type/c10/macros/Macros.h
+' $HEADERS_PATH/executorch/runtime/core/portable_type/c10/c10/macros/Macros.h
 sed -i '' '1i\
 #define C10_USING_CUSTOM_GENERATED_MACROS
-' $HEADERS_PATH/executorch/runtime/core/portable_type/c10/macros/Export.h
-cp -r $HEADERS_PATH/executorch/runtime/core/portable_type/c10 "$HEADERS_PATH/"
+' $HEADERS_PATH/executorch/runtime/core/portable_type/c10/c10/macros/Export.h
+cp -r $HEADERS_PATH/executorch/runtime/core/portable_type/c10/c10 "$HEADERS_PATH/"
 
 
 cp "$SOURCE_ROOT_DIR/extension/apple/ExecuTorch/Exported/"*.h "$HEADERS_PATH/executorch"
diff --git a/build/executorch-config.cmake b/build/executorch-config.cmake
index 40c28d0b961..d14a1227cd9 100644
--- a/build/executorch-config.cmake
+++ b/build/executorch-config.cmake
@@ -29,7 +29,7 @@ cmake_minimum_required(VERSION 3.19)
 set(_root "${CMAKE_CURRENT_LIST_DIR}/../../..")
 set(required_lib_list executorch executorch_core portable_kernels)
 set(EXECUTORCH_LIBRARIES)
-set(EXECUTORCH_INCLUDE_DIRS ${_root}/include ${_root}/include/executorch/runtime/core/portable_type ${_root}/lib)
+set(EXECUTORCH_INCLUDE_DIRS ${_root}/include ${_root}/include/executorch/runtime/core/portable_type/c10 ${_root}/lib)
 foreach(lib ${required_lib_list})
   set(lib_var "LIB_${lib}")
   add_library(${lib} STATIC IMPORTED)
@@ -40,7 +40,7 @@ foreach(lib ${required_lib_list})
   )
   set_target_properties(${lib} PROPERTIES IMPORTED_LOCATION "${${lib_var}}")
   target_compile_definitions(${lib} INTERFACE C10_USING_CUSTOM_GENERATED_MACROS)
-  target_include_directories(${lib} INTERFACE ${_root}/include ${_root}/include/executorch/runtime/core/portable_type ${_root}/lib)
+  target_include_directories(${lib} INTERFACE ${_root}/include ${_root}/include/executorch/runtime/core/portable_type/c10 ${_root}/lib)
   list(APPEND EXECUTORCH_LIBRARIES ${lib})
 endforeach()
 
@@ -110,7 +110,7 @@ foreach(lib ${lib_list})
       add_library(${lib} STATIC IMPORTED)
     endif()
     set_target_properties(${lib} PROPERTIES IMPORTED_LOCATION "${${lib_var}}")
-    target_include_directories(${lib} INTERFACE ${_root}/include ${_root}/include/executorch/runtime/core/portable_type ${_root}/lib)
+    target_include_directories(${lib} INTERFACE ${_root}/include ${_root}/include/executorch/runtime/core/portable_type/c10 ${_root}/lib)
     list(APPEND EXECUTORCH_LIBRARIES ${lib})
   endif()
 endforeach()
diff --git a/examples/apple/coreml/executor_runner/coreml_executor_runner.xcodeproj/project.pbxproj b/examples/apple/coreml/executor_runner/coreml_executor_runner.xcodeproj/project.pbxproj
index 71301f113b2..a4d22670f68 100644
--- a/examples/apple/coreml/executor_runner/coreml_executor_runner.xcodeproj/project.pbxproj
+++ b/examples/apple/coreml/executor_runner/coreml_executor_runner.xcodeproj/project.pbxproj
@@ -298,7 +298,7 @@
 				ENABLE_HARDENED_RUNTIME = YES;
 				HEADER_SEARCH_PATHS = (
                                 	"$(SRCROOT)/include",
-                                	"$(SRCROOT)/include/executorch/runtime/core/portable_type",
+                                	"$(SRCROOT)/include/executorch/runtime/core/portable_type/c10",
                                 );
 				IPHONEOS_DEPLOYMENT_TARGET = 16.0;
 				LIBRARY_SEARCH_PATHS = (
@@ -320,7 +320,7 @@
 				ENABLE_HARDENED_RUNTIME = YES;
 				HEADER_SEARCH_PATHS = (
                                 	"$(SRCROOT)/include",
-                                	"$(SRCROOT)/include/executorch/runtime/core/portable_type",
+                                	"$(SRCROOT)/include/executorch/runtime/core/portable_type/c10",
                                 );
 				IPHONEOS_DEPLOYMENT_TARGET = 16.0;
 				LIBRARY_SEARCH_PATHS = (
diff --git a/examples/arm/executor_runner/CMakeLists.txt b/examples/arm/executor_runner/CMakeLists.txt
index 54da4659a02..d43a7047080 100644
--- a/examples/arm/executor_runner/CMakeLists.txt
+++ b/examples/arm/executor_runner/CMakeLists.txt
@@ -384,7 +384,7 @@ target_link_options( arm_executor_runner PUBLIC LINKER:-Map=arm_executor_runner.
 
 # ET headers and generated headers includes
 target_include_directories(
-  arm_executor_runner PRIVATE ${ET_INCLUDE_PATH} ${ET_DIR_PATH}/runtime/core/portable_type ${CMAKE_CURRENT_BINARY_DIR}
+  arm_executor_runner PRIVATE ${ET_INCLUDE_PATH} ${ET_DIR_PATH}/runtime/core/portable_type/c10 ${CMAKE_CURRENT_BINARY_DIR}
 )
 target_compile_definitions(arm_executor_runner PRIVATE C10_USING_CUSTOM_GENERATED_MACROS)
 
diff --git a/kernels/optimized/cpu/targets.bzl b/kernels/optimized/cpu/targets.bzl
index c556803313e..1c62b683b8f 100644
--- a/kernels/optimized/cpu/targets.bzl
+++ b/kernels/optimized/cpu/targets.bzl
@@ -38,7 +38,7 @@ _OPTIMIZED_ATEN_OPS = (
         name = "op_gelu",
         deps = [
             "//executorch/kernels/portable/cpu/util:activation_ops_util",
-            "//executorch/runtime/core/portable_type/c10:aten_headers_for_executorch",
+            "//executorch/runtime/core/portable_type/c10/c10:aten_headers_for_executorch",
         ],
     ),
     op_target(
diff --git a/runtime/core/portable_type/c10/README.md b/runtime/core/portable_type/c10/README.md
new file mode 100644
index 00000000000..df14d22a4cf
--- /dev/null
+++ b/runtime/core/portable_type/c10/README.md
@@ -0,0 +1,7 @@
+We added an extra c10 directory so that runtime/core/portable_type/c10
+can be the directory to put on your include path, rather than
+runtime/core/portable_type, because using runtime/core/portable_type
+would cause all headers in that directory to be includeable with
+`#include <foo.h>`. In particular, that includes
+runtime/core/portable_type/complex.h, which would shadow the C99
+complex.h standard header.
diff --git a/runtime/core/portable_type/c10/TARGETS b/runtime/core/portable_type/c10/c10/TARGETS
similarity index 100%
rename from runtime/core/portable_type/c10/TARGETS
rename to runtime/core/portable_type/c10/c10/TARGETS
diff --git a/runtime/core/portable_type/c10/macros/Export.h b/runtime/core/portable_type/c10/c10/macros/Export.h
similarity index 100%
rename from runtime/core/portable_type/c10/macros/Export.h
rename to runtime/core/portable_type/c10/c10/macros/Export.h
diff --git a/runtime/core/portable_type/c10/macros/Macros.h b/runtime/core/portable_type/c10/c10/macros/Macros.h
similarity index 100%
rename from runtime/core/portable_type/c10/macros/Macros.h
rename to runtime/core/portable_type/c10/c10/macros/Macros.h
diff --git a/runtime/core/portable_type/c10/targets.bzl b/runtime/core/portable_type/c10/c10/targets.bzl
similarity index 100%
rename from runtime/core/portable_type/c10/targets.bzl
rename to runtime/core/portable_type/c10/c10/targets.bzl
diff --git a/runtime/core/portable_type/c10/util/BFloat16-inl.h b/runtime/core/portable_type/c10/c10/util/BFloat16-inl.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/BFloat16-inl.h
rename to runtime/core/portable_type/c10/c10/util/BFloat16-inl.h
diff --git a/runtime/core/portable_type/c10/util/BFloat16-math.h b/runtime/core/portable_type/c10/c10/util/BFloat16-math.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/BFloat16-math.h
rename to runtime/core/portable_type/c10/c10/util/BFloat16-math.h
diff --git a/runtime/core/portable_type/c10/util/BFloat16.h b/runtime/core/portable_type/c10/c10/util/BFloat16.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/BFloat16.h
rename to runtime/core/portable_type/c10/c10/util/BFloat16.h
diff --git a/runtime/core/portable_type/c10/util/Half-inl.h b/runtime/core/portable_type/c10/c10/util/Half-inl.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/Half-inl.h
rename to runtime/core/portable_type/c10/c10/util/Half-inl.h
diff --git a/runtime/core/portable_type/c10/util/Half.h b/runtime/core/portable_type/c10/c10/util/Half.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/Half.h
rename to runtime/core/portable_type/c10/c10/util/Half.h
diff --git a/runtime/core/portable_type/c10/util/TypeSafeSignMath.h b/runtime/core/portable_type/c10/c10/util/TypeSafeSignMath.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/TypeSafeSignMath.h
rename to runtime/core/portable_type/c10/c10/util/TypeSafeSignMath.h
diff --git a/runtime/core/portable_type/c10/util/bit_cast.h b/runtime/core/portable_type/c10/c10/util/bit_cast.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/bit_cast.h
rename to runtime/core/portable_type/c10/c10/util/bit_cast.h
diff --git a/runtime/core/portable_type/c10/util/floating_point_utils.h b/runtime/core/portable_type/c10/c10/util/floating_point_utils.h
similarity index 100%
rename from runtime/core/portable_type/c10/util/floating_point_utils.h
rename to runtime/core/portable_type/c10/c10/util/floating_point_utils.h
diff --git a/runtime/core/portable_type/targets.bzl b/runtime/core/portable_type/targets.bzl
index 725418cb4ea..43efeca208c 100644
--- a/runtime/core/portable_type/targets.bzl
+++ b/runtime/core/portable_type/targets.bzl
@@ -52,7 +52,7 @@ def define_common_targets():
             "bits_types.h",
         ],
         exported_deps = [
-            "//executorch/runtime/core/portable_type/c10:c10",
+            "//executorch/runtime/core/portable_type/c10/c10:c10",
         ],
         visibility = [
             "//executorch/extension/...",
diff --git a/runtime/core/portable_type/test/CMakeLists.txt b/runtime/core/portable_type/test/CMakeLists.txt
index 6922a8c8fa9..f21e4fc791c 100644
--- a/runtime/core/portable_type/test/CMakeLists.txt
+++ b/runtime/core/portable_type/test/CMakeLists.txt
@@ -19,8 +19,14 @@ set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../../..)
 
 include(${EXECUTORCH_ROOT}/build/Test.cmake)
 
-set(_test_srcs optional_test.cpp tensor_test.cpp half_test.cpp scalar_test.cpp
-               tensor_impl_test.cpp bfloat16_test.cpp
+set(_test_srcs
+    bfloat16_test.cpp
+    dont_shadow_complex_test.c
+    half_test.cpp
+    optional_test.cpp
+    scalar_test.cpp
+    tensor_impl_test.cpp
+    tensor_test.cpp
 )
 
 et_cxx_test(runtime_core_portable_type_test SOURCES ${_test_srcs} EXTRA_LIBS)
diff --git a/runtime/core/portable_type/test/dont_shadow_complex_test.c b/runtime/core/portable_type/test/dont_shadow_complex_test.c
new file mode 100644
index 00000000000..56542166456
--- /dev/null
+++ b/runtime/core/portable_type/test/dont_shadow_complex_test.c
@@ -0,0 +1,9 @@
+// This include statement should get the C99 standard header
+// complex.h. At one point we messed up our c10 include setup such
+// that it instead included runtime/core/portable_type/complex.h. This
+// is a regression test for that issue.
+#include <complex.h>
+
+#ifndef complex
+#warning "complex.h does not define complex"
+#endif
diff --git a/test/utils/OSSTestConfig.json b/test/utils/OSSTestConfig.json
index 2229b255401..6eff74eec86 100644
--- a/test/utils/OSSTestConfig.json
+++ b/test/utils/OSSTestConfig.json
@@ -61,12 +61,13 @@
     {
         "directory": "runtime/core/portable_type/test",
         "sources": [
-            "optional_test.cpp",
-            "tensor_test.cpp",
+            "bfloat16_test.cpp",
+            "dont_shadow_complex_test.c",
             "half_test.cpp",
+            "optional_test.cpp",
             "scalar_test.cpp",
             "tensor_impl_test.cpp",
-            "bfloat16_test.cpp"
+            "tensor_test.cpp"
         ]
     },
     {