diff --git a/llvm/cmake/config.guess b/llvm/cmake/config.guess
--- a/llvm/cmake/config.guess
+++ b/llvm/cmake/config.guess
@@ -816,6 +816,9 @@
     i*:PW*:*)
 	echo ${UNAME_MACHINE}-pc-pw32
 	exit ;;
+    *:SerenityOS:*:*)
+	echo ${UNAME_MACHINE}-pc-serenity
+	exit ;;
     *:Interix*:*)
 	case ${UNAME_MACHINE} in
 	    x86)