diff --git a/cmake/compiler/xcc/target.cmake b/cmake/compiler/xcc/target.cmake
index f9e9c721a15..56d15451d3d 100644
--- a/cmake/compiler/xcc/target.cmake
+++ b/cmake/compiler/xcc/target.cmake
@@ -37,7 +37,22 @@ foreach(file_name include/stddef.h include-fixed/limits.h)
   get_filename_component(_OUTPUT "${_OUTPUT}" DIRECTORY)
   string(REGEX REPLACE "\n" "" _OUTPUT "${_OUTPUT}")
 
-  list(APPEND NOSTDINC ${_OUTPUT})
+  # Need to make sure the path exists before we add it to ${NOSTDINC}.
+  # For example, include-fixed is in xcc but not xt-clang.
+  if(EXISTS "${_OUTPUT}")
+    list(APPEND NOSTDINC ${_OUTPUT})
+
+    if("${ZEPHYR_TOOLCHAIN_VARIANT}" STREQUAL "xt-clang")
+      # This forcibly adds -isystem so that the xt-clang system
+      # include paths are before the xcc include paths.
+      # For some reason, xt-clang places xcc include paths before
+      # xt-clang ones so we need to force it.
+      #
+      # Some modules ignores the compiler property nostdinc_include
+      # so we need to make sure -isystem is used there.
+      add_compile_options(-isystem ${_OUTPUT})
+    endif()
+  endif()
 endforeach()
 
 # This libgcc code is partially duplicated in compiler/*/target.cmake
diff --git a/cmake/compiler/xt-clang/compiler_flags.cmake b/cmake/compiler/xt-clang/compiler_flags.cmake
index c70832ebc0f..54451194c6d 100644
--- a/cmake/compiler/xt-clang/compiler_flags.cmake
+++ b/cmake/compiler/xt-clang/compiler_flags.cmake
@@ -2,25 +2,10 @@
 
 include(${ZEPHYR_BASE}/cmake/compiler/clang/compiler_flags.cmake)
 
-# nostdinc_include contains path to llvm headers and also relative
-# path of "include-fixed".
-# Clear "nostdinc" and nostdinc_include
+# nostdinc needs to be cleared as it is needed for xtensa/config/core.h.
+# nostdinc_include contains path to llvm headers.
 set_compiler_property(PROPERTY nostdinc)
-set_compiler_property(PROPERTY nostdinc_include)
-
-# For C++ code, re-add the standard includes directory which was
-# cleared up from nostdinc_inlcude in above lines with no
-# "include-fixed" this time"
-if(CONFIG_CPP)
-  execute_process(
-    COMMAND ${CMAKE_C_COMPILER} --print-file-name=include/stddef.h
-    OUTPUT_VARIABLE _OUTPUT
-    COMMAND_ERROR_IS_FATAL ANY
-    )
-  get_filename_component(_OUTPUT "${_OUTPUT}" DIRECTORY)
-  string(REGEX REPLACE "\n" "" _OUTPUT "${_OUTPUT}")
-  set_compiler_property(PROPERTY nostdinc_include "${_OUTPUT}")
-endif()
+set_compiler_property(APPEND PROPERTY nostdinc_include ${NOSTDINC})
 
 if($ENV{XCC_NO_G_FLAG})
   # Older xcc/clang cannot use "-g" due to this bug: