diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index c95d7cdeb73ab..576607d576ad1 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -387,7 +387,11 @@ impl<'a> StripUnconfigured<'a> {
             );
 
             if attr.is_doc_comment() {
-                err.help("`///` is for documentation comments. For a plain comment, use `//`.");
+                err.help(if attr.style == AttrStyle::Outer {
+                    "`///` is used for outer documentation comments; for a plain comment, use `//`"
+                } else {
+                    "`//!` is used for inner documentation comments; for a plain comment, use `//` by removing the `!` or inserting a space in between them: `// !`"
+                });
             }
 
             err.emit();
diff --git a/tests/ui/feature-gates/feature-gate-stmt_expr_attributes.stderr b/tests/ui/feature-gates/feature-gate-stmt_expr_attributes.stderr
index 6cca068072254..14f7d58e47aec 100644
--- a/tests/ui/feature-gates/feature-gate-stmt_expr_attributes.stderr
+++ b/tests/ui/feature-gates/feature-gate-stmt_expr_attributes.stderr
@@ -17,7 +17,7 @@ LL |     /// foo
    = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
    = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-   = help: `///` is for documentation comments. For a plain comment, use `//`.
+   = help: `///` is used for outer documentation comments; for a plain comment, use `//`
 
 error[E0658]: attributes on expressions are experimental
   --> $DIR/feature-gate-stmt_expr_attributes.rs:10:5
@@ -28,7 +28,7 @@ LL |     //! foo
    = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
    = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-   = help: `///` is for documentation comments. For a plain comment, use `//`.
+   = help: `//!` is used for inner documentation comments; for a plain comment, use `//` by removing the `!` or inserting a space in between them: `// !`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/lint/unused/unused-doc-comments-edge-cases.stderr b/tests/ui/lint/unused/unused-doc-comments-edge-cases.stderr
index 55e4834e6707a..c074117455493 100644
--- a/tests/ui/lint/unused/unused-doc-comments-edge-cases.stderr
+++ b/tests/ui/lint/unused/unused-doc-comments-edge-cases.stderr
@@ -13,7 +13,7 @@ LL |     /// useless doc comment
    = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
    = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-   = help: `///` is for documentation comments. For a plain comment, use `//`.
+   = help: `///` is used for outer documentation comments; for a plain comment, use `//`
 
 error: unused doc comment
   --> $DIR/unused-doc-comments-edge-cases.rs:6:9