diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 542bc3b02e02b..ec038fada3e9b 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -591,8 +591,7 @@ pub trait PrettyPrinter<'tcx>:
                 p!(")")
             }
             ty::FnDef(def_id, substs) => {
-                let sig = self.tcx().fn_sig(def_id).subst(self.tcx(), substs);
-                p!(print(sig), " {{", print_value_path(def_id, substs), "}}");
+                p!("{{individual function type for ", print_value_path(def_id, substs), "}}");
             }
             ty::FnPtr(ref bare_fn) => p!(print(bare_fn)),
             ty::Infer(infer_ty) => {
diff --git a/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs b/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs
index 79965c1dc2875..edfd995fa5b2d 100644
--- a/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs
+++ b/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs
@@ -32,12 +32,23 @@ impl<'tcx> StructuredDiagnostic<'tcx> for MissingCastForVariadicArg<'tcx> {
         }
 
         if let Ok(snippet) = self.sess.source_map().span_to_snippet(self.span) {
-            err.span_suggestion(
-                self.span,
-                &format!("cast the value to `{}`", self.cast_ty),
-                format!("{} as {}", snippet, self.cast_ty),
-                Applicability::MachineApplicable,
-            );
+            if self.ty.is_fn() {
+                err.span_suggestion(
+                    self.span,
+                    "cast the value to a function pointer",
+                    format!("{} as {}", snippet, self.cast_ty),
+                    Applicability::MachineApplicable,
+                )
+                .help("a function item is zero-sized and needs to be casted to a function pointer to be used in FFI")
+                .note("for more information on function items, visit https://doc.rust-lang.org/reference/types/function-item.html");
+            } else {
+                err.span_suggestion(
+                    self.span,
+                    &format!("cast the value to `{}`", self.cast_ty),
+                    format!("{} as {}", snippet, self.cast_ty),
+                    Applicability::MachineApplicable,
+                );
+            }
         } else {
             err.help(&format!("cast the value to `{}`", self.cast_ty));
         }