diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 1ee535b68b0..cebb9d09a47 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -1168,17 +1168,12 @@ fn cmp_fn_sig(
         let output1 = sig1.output();
         let output2 = sig2.output();
         let (x1, x2) = self.cmp(output1, output2);
-        let only_output_diff = !lifetime_diff
-            && sig1.c_variadic == sig2.c_variadic
-            && sig1.safety == sig2.safety
-            && sig1.abi == sig2.abi
-            && sig1.inputs() == sig2.inputs()
-            && x1 != x2;
-        if !output1.is_unit() || only_output_diff {
+        let output_diff = x1 != x2;
+        if !output1.is_unit() || output_diff {
             values.0.push_normal(" -> ");
             (values.0).0.extend(x1.0);
         }
-        if !output2.is_unit() || only_output_diff {
+        if !output2.is_unit() || output_diff {
             values.1.push_normal(" -> ");
             (values.1).0.extend(x2.0);
         }
diff --git a/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr b/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr
index 06a606b09dc..584724dfe59 100644
--- a/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr
+++ b/tests/ui/feature-gates/feature-gate-unboxed-closures-manual-impls.stderr
@@ -92,7 +92,7 @@ LL |     extern "rust-call" fn call(self, args: ()) -> () {}
    |                                ^^^^ expected `&Foo`, found `Foo`
    |
    = note: expected signature `extern "rust-call" fn(&Foo, ()) -> _`
-              found signature `extern "rust-call" fn(Foo, ())`
+              found signature `extern "rust-call" fn(Foo, ()) -> ()`
 help: change the self-receiver type to match the trait
    |
 LL |     extern "rust-call" fn call(&self, args: ()) -> () {}
@@ -162,7 +162,7 @@ LL |     extern "rust-call" fn call_mut(&self, args: ()) -> () {}
    |                                    ^^^^^ types differ in mutability
    |
    = note: expected signature `extern "rust-call" fn(&mut Bar, ()) -> _`
-              found signature `extern "rust-call" fn(&Bar, ())`
+              found signature `extern "rust-call" fn(&Bar, ()) -> ()`
 help: change the self-receiver type to match the trait
    |
 LL |     extern "rust-call" fn call_mut(&mut self, args: ()) -> () {}
diff --git a/tests/ui/fn/fn_def_opaque_coercion_to_fn_ptr.stderr b/tests/ui/fn/fn_def_opaque_coercion_to_fn_ptr.stderr
index 0b3331b040d..5000601e90f 100644
--- a/tests/ui/fn/fn_def_opaque_coercion_to_fn_ptr.stderr
+++ b/tests/ui/fn/fn_def_opaque_coercion_to_fn_ptr.stderr
@@ -10,7 +10,7 @@ LL |     x = foo::<()>;
    |         ^^^^^^^^^ expected fn item, found a different fn item
    |
    = note: expected fn item `fn(F) -> F {bar::<F>}`
-              found fn item `fn(()) {foo::<()>}`
+              found fn item `fn(()) -> () {foo::<()>}`
 
 error[E0308]: mismatched types
   --> $DIR/fn_def_opaque_coercion_to_fn_ptr.rs:27:9
@@ -26,7 +26,7 @@ LL |     let mut x = bar::<()>;
 LL |     x = foo::<I>;
    |         ^^^^^^^^ expected fn item, found a different fn item
    |
-   = note: expected fn item `fn(()) {bar::<()>}`
+   = note: expected fn item `fn(()) -> () {bar::<()>}`
               found fn item `fn(I) -> I {foo::<I>}`
 help: use parentheses to call this function
    |
diff --git a/tests/ui/impl-trait/trait_type.stderr b/tests/ui/impl-trait/trait_type.stderr
index 0eb132c7a19..989779a6178 100644
--- a/tests/ui/impl-trait/trait_type.stderr
+++ b/tests/ui/impl-trait/trait_type.stderr
@@ -5,7 +5,7 @@ LL |    fn fmt(&self, x: &str) -> () { }
    |                     ^^^^ types differ in mutability
    |
    = note: expected signature `fn(&MyType, &mut Formatter<'_>) -> Result<(), std::fmt::Error>`
-              found signature `fn(&MyType, &str)`
+              found signature `fn(&MyType, &str) -> ()`
 help: change the parameter type to match the trait
    |
 LL |    fn fmt(&self, x: &mut Formatter<'_>) -> () { }
diff --git a/tests/ui/panic-handler/panic-handler-bad-signature-1.stderr b/tests/ui/panic-handler/panic-handler-bad-signature-1.stderr
index 812f7a0692f..4fea52fec6e 100644
--- a/tests/ui/panic-handler/panic-handler-bad-signature-1.stderr
+++ b/tests/ui/panic-handler/panic-handler-bad-signature-1.stderr
@@ -5,7 +5,7 @@ LL | fn panic(info: PanicInfo) -> () {}
    |                ^^^^^^^^^ expected `&PanicInfo<'_>`, found `PanicInfo<'_>`
    |
    = note: expected signature `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
-              found signature `for<'a> fn(PanicInfo<'a>)`
+              found signature `for<'a> fn(PanicInfo<'a>) -> ()`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/traits/impl-method-mismatch.stderr b/tests/ui/traits/impl-method-mismatch.stderr
index 77d542c729a..db457b77a23 100644
--- a/tests/ui/traits/impl-method-mismatch.stderr
+++ b/tests/ui/traits/impl-method-mismatch.stderr
@@ -10,7 +10,7 @@ note: type in trait
 LL |     fn jumbo(&self, x: &usize) -> usize;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: expected signature `fn(&_, &_) -> usize`
-              found signature `unsafe fn(&_, &_)`
+              found signature `unsafe fn(&_, &_) -> ()`
 
 error: aborting due to 1 previous error