diff --git a/gcc/rust/checks/errors/rust-ast-validation.cc b/gcc/rust/checks/errors/rust-ast-validation.cc
index 6fb142c78455..cd197fc1ea7d 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.cc
+++ b/gcc/rust/checks/errors/rust-ast-validation.cc
@@ -103,6 +103,10 @@ ASTValidation::visit (AST::Function &function)
     rust_error_at (function.get_locus (),
 		   "functions cannot be both %<const%> and %<async%>");
 
+  if (qualifiers.is_const () && context.back () == Context::TRAIT_IMPL)
+    rust_error_at (function.get_locus (), ErrorCode::E0379,
+		   "functions in traits cannot be declared const");
+
   if (valid_context.find (context.back ()) == valid_context.end ()
       && function.has_self_param ())
     rust_error_at (
diff --git a/gcc/testsuite/rust/compile/issue-2040.rs b/gcc/testsuite/rust/compile/issue-2040.rs
new file mode 100644
index 000000000000..fbac168b9f38
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2040.rs
@@ -0,0 +1,12 @@
+trait Foo {
+    fn f() -> u32;
+}
+
+impl Foo for u32 {
+    const fn f() -> u32 {
+        // { dg-error "functions in traits cannot be declared const" "" { target *-*-* } .-1 }
+        22
+    }
+}
+
+fn main() {}