diff --git a/tools/pybind11NewTools.cmake b/tools/pybind11NewTools.cmake
index 7d7424a790..3a35a73863 100644
--- a/tools/pybind11NewTools.cmake
+++ b/tools/pybind11NewTools.cmake
@@ -233,11 +233,13 @@ function(pybind11_add_module target_name)
     endif()
   endif()
 
-  # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
-  string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
-  if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
-    # Strip unnecessary sections of the binary on Linux/macOS
-    pybind11_strip(${target_name})
+  if(DEFINED CMAKE_BUILD_TYPE) # see https://github.com/pybind/pybind11/issues/4454
+    # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
+    string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+    if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
+      # Strip unnecessary sections of the binary on Linux/macOS
+      pybind11_strip(${target_name})
+    endif()
   endif()
 
   if(MSVC)
diff --git a/tools/pybind11Tools.cmake b/tools/pybind11Tools.cmake
index 66ad00a478..67e710bda5 100644
--- a/tools/pybind11Tools.cmake
+++ b/tools/pybind11Tools.cmake
@@ -212,10 +212,12 @@ function(pybind11_add_module target_name)
     endif()
   endif()
 
-  # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
-  string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
-  if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
-    pybind11_strip(${target_name})
+  if(DEFINED CMAKE_BUILD_TYPE) # see https://github.com/pybind/pybind11/issues/4454
+    # Use case-insensitive comparison to match the result of $<CONFIG:cfgs>
+    string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+    if(NOT MSVC AND NOT "${uppercase_CMAKE_BUILD_TYPE}" MATCHES DEBUG|RELWITHDEBINFO)
+      pybind11_strip(${target_name})
+    endif()
   endif()
 
   if(MSVC)