diff --git a/mkspecs/features/ltcg.prf b/mkspecs/features/ltcg.prf
index ccf0226272..f2dbc6fa9e 100644
--- a/mkspecs/features/ltcg.prf
+++ b/mkspecs/features/ltcg.prf
@@ -28,7 +28,10 @@ CONFIG(release, debug|release) {
     }
 
     load(link_ltcg)
-    QMAKE_CFLAGS *= $$QMAKE_CFLAGS_LTCG
-    QMAKE_CXXFLAGS *= $$QMAKE_CXXFLAGS_LTCG
-    QMAKE_LFLAGS *= $$QMAKE_LFLAGS_LTCG
+    QMAKE_CFLAGS -= $$QMAKE_CFLAGS_LTCG
+    QMAKE_CFLAGS += $$QMAKE_CFLAGS_LTCG
+    QMAKE_CXXFLAGS -= $$QMAKE_CXXFLAGS_LTCG
+    QMAKE_CXXFLAGS += $$QMAKE_CXXFLAGS_LTCG
+    QMAKE_LFLAGS -= $$QMAKE_LFLAGS_LTCG
+    QMAKE_LFLAGS += $$QMAKE_LFLAGS_LTCG
 }