diff --git a/support/misc/toolchainfile.cmake.in b/support/misc/toolchainfile.cmake.in
index be575566a4..30c0e63bf2 100644
--- a/support/misc/toolchainfile.cmake.in
+++ b/support/misc/toolchainfile.cmake.in
@@ -14,9 +14,15 @@ string(REPLACE "/share/buildroot" "" RELOCATED_HOST_DIR ${CMAKE_CURRENT_LIST_DIR
 # so that it can find our custom platform description.
 list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR})
 
-set(CMAKE_SYSTEM_NAME Buildroot)
-set(CMAKE_SYSTEM_VERSION 1)
-set(CMAKE_SYSTEM_PROCESSOR @@CMAKE_SYSTEM_PROCESSOR@@)
+if(NOT DEFINED CMAKE_SYSTEM_NAME)
+  set(CMAKE_SYSTEM_NAME Buildroot)
+endif()
+if(NOT DEFINED CMAKE_SYSTEM_VERSION)
+  set(CMAKE_SYSTEM_VERSION 1)
+endif()
+if(NOT DEFINED CMAKE_SYSTEM_PROCESSOR)
+  set(CMAKE_SYSTEM_PROCESSOR @@CMAKE_SYSTEM_PROCESSOR@@)
+endif()
 
 # Set the {C,CXX}FLAGS appended by CMake depending on the build type
 # defined by Buildroot. CMake defaults these variables with -g and/or
@@ -28,11 +34,17 @@ set(CMAKE_SYSTEM_PROCESSOR @@CMAKE_SYSTEM_PROCESSOR@@)
 # Note:
 #   if the project forces some of these flag variables, Buildroot is
 #   screwed up and there is nothing Buildroot can do about that :(
-set(CMAKE_C_FLAGS_DEBUG "" CACHE STRING "Debug CFLAGS")
-set(CMAKE_C_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release CFLAGS")
+if(NOT DEFINED CMAKE_C_FLAGS_DEBUG)
+  set(CMAKE_C_FLAGS_DEBUG "" CACHE STRING "Debug CFLAGS")
+endif()
+if(NOT DEFINED CMAKE_C_FLAGS_RELEASE)
+  set(CMAKE_C_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release CFLAGS")
+endif()
 
 # Build type from the Buildroot configuration
-set(CMAKE_BUILD_TYPE @@CMAKE_BUILD_TYPE@@ CACHE STRING "Buildroot build configuration")
+if(NOT DEFINED CMAKE_BUILD_TYPE)
+  set(CMAKE_BUILD_TYPE @@CMAKE_BUILD_TYPE@@ CACHE STRING "Buildroot build configuration")
+endif()
 
 # Buildroot defaults flags.
 # If you are using this toolchainfile.cmake file outside of Buildroot and
@@ -41,33 +53,75 @@ set(CMAKE_BUILD_TYPE @@CMAKE_BUILD_TYPE@@ CACHE STRING "Buildroot build configur
 #     cmake -DCMAKE_C_FLAGS="@@TARGET_CFLAGS@@ -Dsome_custom_flag" ...
 # * and make sure the project's CMake code extends them like this if needed:
 #     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Dsome_definitions")
-set(CMAKE_C_FLAGS "@@TARGET_CFLAGS@@" CACHE STRING "Buildroot CFLAGS")
-set(CMAKE_EXE_LINKER_FLAGS "@@TARGET_LDFLAGS@@" CACHE STRING "Buildroot LDFLAGS for executables")
-set(CMAKE_SHARED_LINKER_FLAGS "@@TARGET_LDFLAGS@@" CACHE STRING "Buildroot LDFLAGS for shared libraries")
-set(CMAKE_MODULE_LINKER_FLAGS "@@TARGET_LDFLAGS@@" CACHE STRING "Buildroot LDFLAGS for module libraries")
+if(NOT DEFINED CMAKE_C_FLAGS)
+  set(CMAKE_C_FLAGS "@@TARGET_CFLAGS@@" CACHE STRING "Buildroot CFLAGS")
+endif()
+if(NOT DEFINED CMAKE_EXE_LINKER_FLAGS)
+  set(CMAKE_EXE_LINKER_FLAGS "@@TARGET_LDFLAGS@@" CACHE STRING "Buildroot LDFLAGS for executables")
+endif()
+if(NOT DEFINED CMAKE_SHARED_LINKER_FLAGS)
+  set(CMAKE_SHARED_LINKER_FLAGS "@@TARGET_LDFLAGS@@" CACHE STRING "Buildroot LDFLAGS for shared libraries")
+endif()
+if(NOT DEFINED CMAKE_MODULE_LINKER_FLAGS)
+  set(CMAKE_MODULE_LINKER_FLAGS "@@TARGET_LDFLAGS@@" CACHE STRING "Buildroot LDFLAGS for module libraries")
+endif()
 
-set(CMAKE_INSTALL_SO_NO_EXE 0)
+if(NOT DEFINED CMAKE_INSTALL_SO_NO_EXE)
+  set(CMAKE_INSTALL_SO_NO_EXE 0)
+endif()
 
-set(CMAKE_PROGRAM_PATH "${RELOCATED_HOST_DIR}/bin")
-set(CMAKE_SYSROOT "${RELOCATED_HOST_DIR}/@@STAGING_SUBDIR@@")
-set(CMAKE_FIND_ROOT_PATH "${RELOCATED_HOST_DIR}/@@STAGING_SUBDIR@@")
-set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
-set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+if(NOT DEFINED CMAKE_PROGRAM_PATH)
+  set(CMAKE_PROGRAM_PATH "${RELOCATED_HOST_DIR}/bin")
+endif()
+if(NOT DEFINED CMAKE_SYSROOT)
+  set(CMAKE_SYSROOT "${RELOCATED_HOST_DIR}/@@STAGING_SUBDIR@@")
+endif()
+if(NOT DEFINED CMAKE_FIND_ROOT_PATH)
+  set(CMAKE_FIND_ROOT_PATH "${RELOCATED_HOST_DIR}/@@STAGING_SUBDIR@@")
+endif()
+if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_PROGRAM)
+  set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+endif()
+if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_PACKAGE)
+  set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+endif()
+if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_LIBRARY)
+  set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+endif()
+if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_INCLUDE)
+  set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+endif()
 set(ENV{PKG_CONFIG_SYSROOT_DIR} "${RELOCATED_HOST_DIR}/@@STAGING_SUBDIR@@")
 
 # This toolchain file can be used both inside and outside Buildroot.
-set(CMAKE_C_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_CC@@")
+if(NOT DEFINED CMAKE_C_COMPILER)
+  set(CMAKE_C_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_CC@@")
+endif()
 if(@@TOOLCHAIN_HAS_CXX@@)
-  set(CMAKE_CXX_FLAGS_DEBUG "" CACHE STRING "Debug CXXFLAGS")
-  set(CMAKE_CXX_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release CXXFLAGS")
-  set(CMAKE_CXX_FLAGS "@@TARGET_CXXFLAGS@@" CACHE STRING "Buildroot CXXFLAGS")
-  set(CMAKE_CXX_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_CXX@@")
+  if(NOT DEFINED CMAKE_CXX_FLAGS_DEBUG)
+    set(CMAKE_CXX_FLAGS_DEBUG "" CACHE STRING "Debug CXXFLAGS")
+  endif()
+  if(NOT DEFINED CMAKE_CXX_FLAGS_RELEASE)
+    set(CMAKE_CXX_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release CXXFLAGS")
+  endif()
+  if(NOT DEFINED CMAKE_CXX_FLAGS)
+    set(CMAKE_CXX_FLAGS "@@TARGET_CXXFLAGS@@" CACHE STRING "Buildroot CXXFLAGS")
+  endif()
+  if(NOT DEFINED CMAKE_CXX_COMPILER)
+    set(CMAKE_CXX_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_CXX@@")
+  endif()
 endif()
 if(@@TOOLCHAIN_HAS_FORTRAN@@)
-  set(CMAKE_Fortran_FLAGS_DEBUG "" CACHE STRING "Debug Fortran FLAGS")
-  set(CMAKE_Fortran_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release Fortran FLAGS")
-  set(CMAKE_Fortran_FLAGS "@@TARGET_FCFLAGS@@" CACHE STRING "Buildroot FCFLAGS")
-  set(CMAKE_Fortran_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_FC@@")
+  if(NOT DEFINED CMAKE_Fortran_FLAGS_DEBUG)
+    set(CMAKE_Fortran_FLAGS_DEBUG "" CACHE STRING "Debug Fortran FLAGS")
+  endif()
+  if(NOT DEFINED CMAKE_Fortran_FLAGS_RELEASE)
+    set(CMAKE_Fortran_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release Fortran FLAGS")
+  endif()
+  if(NOT DEFINED CMAKE_Fortran_FLAGS)
+    set(CMAKE_Fortran_FLAGS "@@TARGET_FCFLAGS@@" CACHE STRING "Buildroot FCFLAGS")
+  endif()
+  if(NOT DEFINED CMAKE_Fortran_COMPILER)
+    set(CMAKE_Fortran_COMPILER "${RELOCATED_HOST_DIR}/@@TARGET_FC@@")
+  endif()
 endif()