diff --git a/src/shared/clang/clang_installation.pri b/src/shared/clang/clang_installation.pri
index 8f102279d4d..afa21e23cec 100644
--- a/src/shared/clang/clang_installation.pri
+++ b/src/shared/clang/clang_installation.pri
@@ -216,7 +216,7 @@ isEmpty(LLVM_VERSION) {
 
     # Remove unwanted flags. It is a workaround for linking.
     # It is not intended for cross compiler linking.
-    LLVM_CXXFLAGS = $$system($$llvm_config --cxxflags, lines)
+    LLVM_CXXFLAGS *= $$system($$llvm_config --cxxflags, lines)
     LLVM_CXXFLAGS ~= s,-fno-exceptions,
     LLVM_CXXFLAGS ~= s,-std=c++11,
     LLVM_CXXFLAGS ~= s,-std=c++0x,
diff --git a/tests/unit/unittest/clang_dependency.pri b/tests/unit/unittest/clang_dependency.pri
index 744c9ff4283..2c72feadff0 100644
--- a/tests/unit/unittest/clang_dependency.pri
+++ b/tests/unit/unittest/clang_dependency.pri
@@ -22,7 +22,7 @@ include(../../../src/shared/clang/clang_defines.pri)
     !contains(QMAKE_DEFAULT_LIBDIRS, $$LLVM_LIBDIR): QMAKE_RPATHDIR += $$LLVM_LIBDIR
 
     LLVM_CXXFLAGS ~= s,-g\d?,
-    QMAKE_CXXFLAGS += $$LLVM_CXXFLAGS
+    QMAKE_CXXFLAGS *= $$LLVM_CXXFLAGS
 
     DEFINES += CLANG_COMPILER_PATH=\"R\\\"xxx($$LLVM_BINDIR/clang)xxx\\\"\"
 }