diff --git a/lib/spack/spack/compilers/clang.py b/lib/spack/spack/compilers/clang.py
index 658884b5de4587..352e842412a350 100644
--- a/lib/spack/spack/compilers/clang.py
+++ b/lib/spack/spack/compilers/clang.py
@@ -151,7 +151,7 @@ def cxx17_flag(self):
                 raise UnsupportedCompilerFlag(self,
                                               "the C++17 standard",
                                               "cxx17_flag",
-                                              "< 5.0")
+                                              "< 3.5")
             elif self.version < ver('5.0'):
                 return "-std=c++1z"
             else:
@@ -167,7 +167,7 @@ def c11_flag(self):
             raise UnsupportedCompilerFlag(self,
                                           "the C11 standard",
                                           "c11_flag",
-                                          "< 3.3")
+                                          "< 6.1.0")
         else:
             return "-std=c11"