--- a/src/3rdparty/mapbox-gl-native/mapbox-gl-native.pro
+++ b/src/3rdparty/mapbox-gl-native/mapbox-gl-native.pro
@@ -57,6 +57,8 @@ TR_EXCLUDE += $$PWD/*
 
 qtConfig(icu) {
     QMAKE_USE_PRIVATE += icu
+    # only the ICU C API is used, the C++ API requires C++17
+    DEFINES += U_SHOW_CPLUSPLUS_API=0
 
     SOURCES += \
         platform/default/bidi.cpp