diff --git a/mkspecs/features/qt_build_config.prf b/mkspecs/features/qt_build_config.prf
index 0c6c10dded..8a7c9c28d3 100644
--- a/mkspecs/features/qt_build_config.prf
+++ b/mkspecs/features/qt_build_config.prf
@@ -37,8 +37,10 @@ intel_icl {
 
 QMAKE_DIR_REPLACE_SANE = PRECOMPILED_DIR OBJECTS_DIR MOC_DIR RCC_DIR UI_DIR
 
+load(qt_prefix_build_check)
+
 # force_independent can be set externally. prefix_build not.
-!exists($$[QT_HOST_DATA]/.qmake.cache): \
+qtIsPrefixBuild($$[QT_HOST_DATA]): \
     CONFIG += prefix_build force_independent
 
 !build_pass:!isEmpty(_QMAKE_SUPER_CACHE_):force_independent {
diff --git a/mkspecs/features/qt_configure.prf b/mkspecs/features/qt_configure.prf
index 95e54d72c9..242544d41b 100644
--- a/mkspecs/features/qt_configure.prf
+++ b/mkspecs/features/qt_configure.prf
@@ -2502,17 +2502,19 @@ logn("Configure summary:")
 logn()
 qtConfPrintReport()
 
+load(qt_prefix_build_check)
+
 # final notes for the user
 logn()
 logn("Qt is now configured for building. Just run '$$QMAKE_MAKE_NAME'.")
 pfx = $$[QT_INSTALL_PREFIX]
-exists($$pfx/.qmake.cache) {
+qtIsPrefixBuild($$pfx) {
+    logn("Once everything is built, you must run '$$QMAKE_MAKE_NAME install'.")
+    logn("Qt will be installed into '$$system_path($$pfx)'.")
+} else {
     logn("Once everything is built, Qt is installed.")
     logn("You should NOT run '$$QMAKE_MAKE_NAME install'.")
     logn("Note that this build cannot be deployed to other machines or devices.")
-} else {
-    logn("Once everything is built, you must run '$$QMAKE_MAKE_NAME install'.")
-    logn("Qt will be installed into '$$system_path($$pfx)'.")
 }
 logn()
 logn("Prior to reconfiguration, make sure you remove any leftovers from")
diff --git a/mkspecs/features/qt_prefix_build_check.prf b/mkspecs/features/qt_prefix_build_check.prf
new file mode 100644
index 0000000000..3f98847de9
--- /dev/null
+++ b/mkspecs/features/qt_prefix_build_check.prf
@@ -0,0 +1,21 @@
+#
+#  W A R N I N G
+#  -------------
+#
+# This file is not part of the Qt API.  It exists purely as an
+# implementation detail.  It may change from version to version
+# without notice, or even be removed.
+#
+# We mean it.
+#
+
+defineTest(qtIsPrefixBuild) {
+    prefixdir = $$1
+    # qtbase non-prefix build?
+    exists($$prefixdir/.qmake.cache): \
+        return(false)
+    # top-level non-prefix build?
+    contains(prefixdir, .*/qtbase):exists($$dirname(prefixdir)/.qmake.super): \
+        return(false)
+    return(true)
+}