diff --git a/acinclude.m4.in b/acinclude.m4.in
index b35aaea..f0bdaa0 100644
--- a/acinclude.m4.in
+++ b/acinclude.m4.in
@@ -4956,7 +4956,7 @@ AC_DEFUN([KDE_CHECK_STL],
     AC_LANG_CPLUSPLUS
     ac_save_CXXFLAGS="$CXXFLAGS"
     CXXFLAGS="`echo $CXXFLAGS | sed s/-fno-exceptions//`"
-    if test -z "$PKG_CONFIG"; then
+    if test -z "$qt_includes"; then
       CXXFLAGS="$CXXFLAGS"
     else
       CXXFLAGS="$CXXFLAGS -I$qt_includes"