diff --git a/gcc/rust/ast/rust-ast.cc b/gcc/rust/ast/rust-ast.cc
index 337a338f9a3..6b79f7b70d8 100644
--- a/gcc/rust/ast/rust-ast.cc
+++ b/gcc/rust/ast/rust-ast.cc
@@ -3834,6 +3834,9 @@ MetaItemLitExpr::check_cfg_predicate (const Session &) const
 {
   /* as far as I can tell, a literal expr can never be a valid cfg body, so
    * false */
+  rust_error_at (this->get_locus (), "'%s' predicate key cannot be a literal",
+		 this->as_string ().c_str ());
+
   return false;
 }
 
diff --git a/gcc/testsuite/rust/compile/issue-4222.rs b/gcc/testsuite/rust/compile/issue-4222.rs
new file mode 100644
index 00000000000..b829c6f6f54
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-4222.rs
@@ -0,0 +1,3 @@
+#![cfg(false)]
+// { dg-error ".false. predicate key cannot be a literal" "" { target *-*-* } .-1 }
+fn a() {}