diff --git a/mkspecs/features/externals.pri b/mkspecs/features/externals.pri
index 607ef1de3..e83eade80 100644
--- a/mkspecs/features/externals.pri
+++ b/mkspecs/features/externals.pri
@@ -21,26 +21,20 @@ isEmpty(EXTERNALSROOT) {
 # Externals
 ################################
 
-EXTERNALS_SPEC = $$basename(QMAKESPEC)
-msvc {
-    clang_cl: EXTERNALS_SPEC = win32-msvc
-    win32-msvc {
-        # From Qt 5.8.1 onwards, QMAKESPEC is win32-msvc without the version number
-        # see https://codereview.qt-project.org/#/c/162754/
-        lessThan(MSVC_VER, 14.0) | greaterThan(MSVC_VER, 15.0) {
-            error(This version of Visual Studio is not supported (MSVC_VER = $$MSVC_VER))
-        }
-    }
-}
+win32-clang-msvc: EXTERNALS_SPEC = win32-msvc
+else:             EXTERNALS_SPEC = $$basename(QMAKESPEC)
 
-win32 {
+msvc {
     INCLUDEPATH *= $$EXTERNALSROOT/common/include
 }
+else:mingw {
+    QMAKE_CXXFLAGS += -isystem $$EXTERNALSROOT/common/include
+}
 else:macx {
     INCLUDEPATH *= $$EXTERNALSROOT/common/include
 }
-else:unix: {
-    QMAKE_CXXFLAGS *= -idirafter $$EXTERNALSROOT/common/include
+else {
+    QMAKE_CXXFLAGS += -idirafter $$EXTERNALSROOT/common/include
 }
 
 equals(WORD_SIZE,64) {