diff --git a/.prev_configure.cmake b/.prev_configure.cmake
index 1ee218646b..3390c85588 100644
--- a/.prev_configure.cmake
+++ b/.prev_configure.cmake
@@ -621,18 +621,19 @@ if(CMAKE_INTERPROCEDURAL_OPTIMIZATION)
     set(__qt_ltcg_detected TRUE)
 else()
     foreach(config ${CMAKE_BUILD_TYPE} ${CMAKE_CONFIGURATION_TYPES})
-        if(CMAKE_INTERPROCEDURAL_OPTIMIZATION_${config})
+        string(TOUPPER "${config}" __qt_uc_config)
+        if(CMAKE_INTERPROCEDURAL_OPTIMIZATION_${__qt_uc_config})
             set(__qt_ltcg_detected TRUE)
             break()
         endif()
     endforeach()
+    unset(__qt_uc_config)
 endif()
 qt_feature("ltcg"
     LABEL "Using LTCG"
     AUTODETECT ON
     CONDITION __qt_ltcg_detected
 )
-unset(__qt_ltcg_detected)
 qt_feature_config("ltcg" QMAKE_PRIVATE_CONFIG)
 qt_feature("enable_gdb_index"
     LABEL "Generating GDB index"
diff --git a/configure.cmake b/configure.cmake
index 984fe4b78a..0aceaaf905 100644
--- a/configure.cmake
+++ b/configure.cmake
@@ -634,18 +634,19 @@ if(CMAKE_INTERPROCEDURAL_OPTIMIZATION)
     set(__qt_ltcg_detected TRUE)
 else()
     foreach(config ${CMAKE_BUILD_TYPE} ${CMAKE_CONFIGURATION_TYPES})
-        if(CMAKE_INTERPROCEDURAL_OPTIMIZATION_${config})
+        string(TOUPPER "${config}" __qt_uc_config)
+        if(CMAKE_INTERPROCEDURAL_OPTIMIZATION_${__qt_uc_config})
             set(__qt_ltcg_detected TRUE)
             break()
         endif()
     endforeach()
+    unset(__qt_uc_config)
 endif()
 qt_feature("ltcg"
     LABEL "Using LTCG"
     AUTODETECT ON
     CONDITION __qt_ltcg_detected
 )
-unset(__qt_ltcg_detected)
 qt_feature_config("ltcg" QMAKE_PRIVATE_CONFIG)
 qt_feature("enable_gdb_index"
     LABEL "Generating GDB index"
diff --git a/util/cmake/configurejson2cmake.py b/util/cmake/configurejson2cmake.py
index d81121b98f..29afd777e7 100755
--- a/util/cmake/configurejson2cmake.py
+++ b/util/cmake/configurejson2cmake.py
@@ -920,14 +920,15 @@ if(CMAKE_INTERPROCEDURAL_OPTIMIZATION)
     set(__qt_ltcg_detected TRUE)
 else()
     foreach(config ${CMAKE_BUILD_TYPE} ${CMAKE_CONFIGURATION_TYPES})
-        if(CMAKE_INTERPROCEDURAL_OPTIMIZATION_${config})
+        string(TOUPPER "${config}" __qt_uc_config)
+        if(CMAKE_INTERPROCEDURAL_OPTIMIZATION_${__qt_uc_config})
             set(__qt_ltcg_detected TRUE)
             break()
         endif()
     endforeach()
+    unset(__qt_uc_config)
 endif()""",
-            "condition": "__qt_ltcg_detected",
-            "cmakeEpilogue": "unset(__qt_ltcg_detected)"
+            "condition": "__qt_ltcg_detected"
         },
         "msvc_mp": None,
         "simulator_and_device": {"condition": "UIKIT AND NOT QT_UIKIT_SDK"},