diff --git a/lib/spack/spack/compilers/gcc.py b/lib/spack/spack/compilers/gcc.py
index ae8d5aa97ef..adef8a8277d 100644
--- a/lib/spack/spack/compilers/gcc.py
+++ b/lib/spack/spack/compilers/gcc.py
@@ -99,6 +99,28 @@ def cxx17_flag(self):
         else:
             return "-std=c++17"
 
+    @property
+    def cxx20_flag(self):
+        if self.real_version < Version("8.0"):
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C++20 standard", "cxx20_flag", "< 8.0"
+            )
+        elif self.real_version < Version("11.0"):
+            return "-std=c++2a"
+        else:
+            return "-std=c++20"
+
+    @property
+    def cxx23_flag(self):
+        if self.real_version < Version("11.0"):
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C++23 standard", "cxx23_flag", "< 11.0"
+            )
+        elif self.real_version < Version("14.0"):
+            return "-std=c++2b"
+        else:
+            return "-std=c++23"
+
     @property
     def c99_flag(self):
         if self.real_version < Version("4.5"):