diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 37e03ddbab12..c3b8aac220a8 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -2923,8 +2923,8 @@ pub(super) fn check_fn_front_matter(&mut self, check_pub: bool, case: Case) -> b
                         && !self.is_unsafe_foreign_mod()
                         // Rule out `async gen {` and `async gen move {`
                         && !self.is_async_gen_block()
-                        // Rule out `const unsafe auto` and `const unsafe trait`.
-                        && !self.is_keyword_ahead(2, &[kw::Auto, kw::Trait])
+                        // Rule out `const unsafe auto` and `const unsafe trait` and `const unsafe impl`.
+                        && !self.is_keyword_ahead(2, &[kw::Auto, kw::Trait, kw::Impl])
                     )
                 })
             // `extern ABI fn`