diff --git a/tools/pybind11NewTools.cmake b/tools/pybind11NewTools.cmake
index 8cee2d4609..e729181551 100644
--- a/tools/pybind11NewTools.cmake
+++ b/tools/pybind11NewTools.cmake
@@ -73,15 +73,17 @@ if(NOT DEFINED ${_Python}_EXECUTABLE)
 
 endif()
 
-if(NOT ${_Python}_EXECUTABLE STREQUAL PYBIND11_PYTHON_EXECUTABLE_LAST)
+if(DEFINED PYBIND11_PYTHON_EXECUTABLE_LAST AND NOT ${_Python}_EXECUTABLE STREQUAL
+                                               PYBIND11_PYTHON_EXECUTABLE_LAST)
   # Detect changes to the Python version/binary in subsequent CMake runs, and refresh config if needed
   unset(PYTHON_IS_DEBUG CACHE)
   unset(PYTHON_MODULE_EXTENSION CACHE)
-  set(PYBIND11_PYTHON_EXECUTABLE_LAST
-      "${${_Python}_EXECUTABLE}"
-      CACHE INTERNAL "Python executable during the last CMake run")
 endif()
 
+set(PYBIND11_PYTHON_EXECUTABLE_LAST
+    "${${_Python}_EXECUTABLE}"
+    CACHE INTERNAL "Python executable during the last CMake run")
+
 if(NOT DEFINED PYTHON_IS_DEBUG)
   # Debug check - see https://stackoverflow.com/questions/646518/python-how-to-detect-debug-Interpreter
   execute_process(