diff --git a/Tools/testflags.py b/Tools/testflags.py
index 981e8d59a..31ca2e7bd 100755
--- a/Tools/testflags.py
+++ b/Tools/testflags.py
@@ -46,7 +46,7 @@ def get_cxxflags(language, std, compiler):
            "php":"-Werror " + cxx_common,
         "python":"-Werror " + cxx_common,
              "r":"-Werror " + cxx_common,
-          "ruby":"-Werror " + cxx_common,
+          "ruby":"-Werror " + cxx_common + "-Wno-deprecated-declarations", # For Ruby on MacOS Xcode 9.4 misconfiguration defining 'isfinite' to deprecated 'finite'
         "scilab":"-Werror " + cxx_common,
            "tcl":"-Werror " + cxx_common,
     }