diff --git a/admin/acinclude.m4.in b/admin/acinclude.m4.in
index aee3f3d..b35aaea 100644
--- a/admin/acinclude.m4.in
+++ b/admin/acinclude.m4.in
@@ -4956,7 +4956,11 @@ AC_DEFUN([KDE_CHECK_STL],
     AC_LANG_CPLUSPLUS
     ac_save_CXXFLAGS="$CXXFLAGS"
     CXXFLAGS="`echo $CXXFLAGS | sed s/-fno-exceptions//`"
-    CXXFLAGS="$CXXFLAGS -I$qt_includes"
+    if test -z "$PKG_CONFIG"; then
+      CXXFLAGS="$CXXFLAGS"
+    else
+      CXXFLAGS="$CXXFLAGS -I$qt_includes"
+    fi
 
     AC_MSG_CHECKING([if C++ programs can be compiled])
     AC_CACHE_VAL(kde_cv_stl_works,