--- a/security/sandbox/linux/moz.build
+++ b/security/sandbox/linux/moz.build
@@ -78,17 +78,17 @@ if CONFIG['MOZ_GMP_SANDBOX']:
     ]
 
 # This copy of SafeSPrintf doesn't need to avoid the Chromium logging
 # dependency like the one in libxul does, but this way the behavior is
 # consistent.  See also the comment in SandboxLogging.h.
 SOURCES['../chromium/base/strings/safe_sprintf.cc'].flags += ['-DNDEBUG']
 
 # Keep clang from warning about intentional 'switch' fallthrough in icu_utf.cc:
-if CONFIG['CLANG_CXX']:
+if CONFIG['CLANG_CXX'] or CONFIG['GNU_CXX']:
     SOURCES['../chromium/base/third_party/icu/icu_utf.cc'].flags += ['-Wno-implicit-fallthrough']
 
 if CONFIG['GNU_CXX']:
     CXXFLAGS += ['-Wno-shadow']
     SOURCES['../chromium/sandbox/linux/services/syscall_wrappers.cc'].flags += [
         '-Wno-empty-body',
     ]