diff --git a/cmake/fetch_llvm.cmake b/cmake/fetch_llvm.cmake
index deb82580..c94c669e 100644
--- a/cmake/fetch_llvm.cmake
+++ b/cmake/fetch_llvm.cmake
@@ -5,22 +5,16 @@
 # top level to any library builds to prevent repeated checkouts.
 
 include(FetchContent)
+include(${CMAKE_CURRENT_LIST_DIR}/patch_repo.cmake)
 
 if(NOT VERSIONS_JSON)
     include(${CMAKE_CURRENT_LIST_DIR}/read_versions.cmake)
 endif()
 read_repo_version(llvmproject llvm-project)
-
-set(patch_script ${CMAKE_CURRENT_LIST_DIR}/patch_repo.py)
-if(GIT_PATCH_METHOD STREQUAL "am")
-    set(patch_script_args --method am)
-elseif(GIT_PATCH_METHOD STREQUAL "apply")
-    set(patch_script_args --method apply)
-endif()
-set(patch_dir ${CMAKE_CURRENT_LIST_DIR}/../patches)
-set(LLVM_PATCH_COMMAND ${Python3_EXECUTABLE} ${patch_script} ${patch_script_args} ${patch_dir}/llvm-project)
+get_patch_command(llvm-project llvm_patch_command)
 if(APPLY_LLVM_PERFORMANCE_PATCHES)
-    set(LLVM_PATCH_COMMAND ${LLVM_PATCH_COMMAND} && ${Python3_EXECUTABLE} ${patch_script} ${patch_script_args} ${patch_dir}/llvm-project-perf)
+    get_patch_command(llvm-project-perf llvm_perf_patch_command)
+    set(llvm_patch_command ${llvm_patch_command} && ${llvm_perf_patch_command} )
 endif()
 
 FetchContent_Declare(llvmproject
@@ -28,7 +22,7 @@ FetchContent_Declare(llvmproject
     GIT_TAG "${llvmproject_TAG}"
     GIT_SHALLOW "${llvmproject_SHALLOW}"
     GIT_PROGRESS TRUE
-    PATCH_COMMAND ${LLVM_PATCH_COMMAND}
+    PATCH_COMMAND ${llvm_patch_command}
     # Add the llvm subdirectory later to ensure that
     # LLVMEmbeddedToolchainForArm is the first project declared.
     # Otherwise CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT
diff --git a/cmake/fetch_newlib.cmake b/cmake/fetch_newlib.cmake
index b3b621ee..e0f20def 100644
--- a/cmake/fetch_newlib.cmake
+++ b/cmake/fetch_newlib.cmake
@@ -5,27 +5,20 @@
 # top level to any library builss to prevent repeated checkouts.
 
 include(FetchContent)
+include(${CMAKE_CURRENT_LIST_DIR}/patch_repo.cmake)
 
 if(NOT VERSIONS_JSON)
     include(${CMAKE_CURRENT_LIST_DIR}/read_versions.cmake)
 endif()
 read_repo_version(newlib newlib)
-
-set(patch_script ${CMAKE_CURRENT_LIST_DIR}/patch_repo.py)
-if(GIT_PATCH_METHOD STREQUAL "am")
-    set(patch_script_args --method am)
-elseif(GIT_PATCH_METHOD STREQUAL "apply")
-    set(patch_script_args --method apply)
-endif()
-set(patch_dir ${CMAKE_CURRENT_LIST_DIR}/../patches)
-set(NEWLIB_PATCH_COMMAND ${Python3_EXECUTABLE} ${patch_script} ${patch_script_args} ${patch_dir}/newlib)
+get_patch_command(newlib newlib_patch_command)
 
 FetchContent_Declare(newlib
     GIT_REPOSITORY https://sourceware.org/git/newlib-cygwin.git
     GIT_TAG "${newlib_TAG}"
     GIT_SHALLOW "${newlib_SHALLOW}"
     GIT_PROGRESS TRUE
-    PATCH_COMMAND ${NEWLIB_PATCH_COMMAND}
+    PATCH_COMMAND ${newlib_patch_command}
     # Similarly to picolibc, we don't do the configuration here.
     SOURCE_SUBDIR do_not_add_newlib_subdir
 )
diff --git a/cmake/fetch_picolibc.cmake b/cmake/fetch_picolibc.cmake
index f0ad368f..4dabc459 100644
--- a/cmake/fetch_picolibc.cmake
+++ b/cmake/fetch_picolibc.cmake
@@ -5,27 +5,20 @@
 # top level to any library builss to prevent repeated checkouts.
 
 include(FetchContent)
+include(${CMAKE_CURRENT_LIST_DIR}/patch_repo.cmake)
 
 if(NOT VERSIONS_JSON)
     include(${CMAKE_CURRENT_LIST_DIR}/read_versions.cmake)
 endif()
 read_repo_version(picolibc picolibc)
-
-set(patch_script ${CMAKE_CURRENT_LIST_DIR}/patch_repo.py)
-if(GIT_PATCH_METHOD STREQUAL "am")
-    set(patch_script_args --method am)
-elseif(GIT_PATCH_METHOD STREQUAL "apply")
-    set(patch_script_args --method apply)
-endif()
-set(patch_dir ${CMAKE_CURRENT_LIST_DIR}/../patches)
-set(PICOLIBC_PATCH_COMMAND ${Python3_EXECUTABLE} ${patch_script} ${patch_script_args} ${patch_dir}/picolibc)
+get_patch_command(picolibc picolibc_patch_command)
 
 FetchContent_Declare(picolibc
     GIT_REPOSITORY https://github.com/picolibc/picolibc.git
     GIT_TAG "${picolibc_TAG}"
     GIT_SHALLOW "${picolibc_SHALLOW}"
     GIT_PROGRESS TRUE
-    PATCH_COMMAND ${PICOLIBC_PATCH_COMMAND}
+    PATCH_COMMAND ${picolibc_patch_command}
     # We only want to download the content, not configure it at this
     # stage. picolibc will be built in many configurations using
     # ExternalProject_Add using the sources that are checked out here.
diff --git a/cmake/patch_repo.cmake b/cmake/patch_repo.cmake
new file mode 100644
index 00000000..c0677f72
--- /dev/null
+++ b/cmake/patch_repo.cmake
@@ -0,0 +1,16 @@
+
+# Function to generate a PATCH_COMMAND, calling the
+# patch_repo.py script using a target set of patches.
+
+function(get_patch_command patch_dir patch_command_out)
+    set(patch_script ${CMAKE_CURRENT_LIST_DIR}/patch_repo.py)
+    list(APPEND patch_script_args ${Python3_EXECUTABLE} ${patch_script})
+    if(GIT_PATCH_METHOD STREQUAL "am")
+        list(APPEND patch_script_args "--method" "am")
+    elseif(GIT_PATCH_METHOD STREQUAL "apply")
+        list(APPEND patch_script_args "--method" "apply")
+    endif()
+    list(APPEND patch_script_args ${CMAKE_CURRENT_LIST_DIR}/../patches/${patch_dir})
+
+    set(${patch_command_out} ${patch_script_args} PARENT_SCOPE)
+endfunction()