diff --git a/compiler/rustc_infer/src/infer/opaque_types/mod.rs b/compiler/rustc_infer/src/infer/opaque_types/mod.rs
index 2bc006c37dac9..d65ed72a8e84b 100644
--- a/compiler/rustc_infer/src/infer/opaque_types/mod.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types/mod.rs
@@ -432,7 +432,6 @@ where
                     upvar.visit_with(self);
                 }
 
-                // FIXME(async_closures): Is this the right signature to visit here?
                 args.as_coroutine_closure().signature_parts_ty().visit_with(self);
             }
 
diff --git a/tests/ui/async-await/async-closures/mangle.rs b/tests/ui/async-await/async-closures/mangle.rs
index 632f1657436ac..a428905e40b72 100644
--- a/tests/ui/async-await/async-closures/mangle.rs
+++ b/tests/ui/async-await/async-closures/mangle.rs
@@ -5,9 +5,6 @@
 //@[v0] compile-flags: -Csymbol-mangling-version=v0
 //@[legacy] compile-flags: -Csymbol-mangling-version=legacy -Zunstable-options
 
-// FIXME(async_closures): When `fn_sig_for_fn_abi` is fixed, remove this.
-//@ ignore-pass (test emits codegen-time warnings)
-
 #![feature(async_closure, noop_waker)]
 
 extern crate block_on;
diff --git a/tests/ui/async-await/async-closures/no-borrow-from-env.rs b/tests/ui/async-await/async-closures/no-borrow-from-env.rs
index fe84aeeb32f7f..3f9d26b971302 100644
--- a/tests/ui/async-await/async-closures/no-borrow-from-env.rs
+++ b/tests/ui/async-await/async-closures/no-borrow-from-env.rs
@@ -38,7 +38,10 @@ fn through_field_and_ref<'a>(x: &S<'a>) {
 
     let c = async move || { println!("{}", *x.0); };
     outlives::<'a>(c());
-    // outlives::<'a>(call_once(c)); // FIXME(async_closures): Figure out why this fails
+
+    // outlives::<'a>(call_once(c));
+    // The above fails b/c the by-move coroutine of `c` captures `x` in its entirety.
+    // Since we have not asserted that the borrow for `&S<'a>` outlives `'a`, it'll fail.
 }
 
 fn main() {}
diff --git a/tests/ui/async-await/async-closures/not-fn.rs b/tests/ui/async-await/async-closures/not-fn.rs
index 5322a6d5d7ad3..5f2d047c3e982 100644
--- a/tests/ui/async-await/async-closures/not-fn.rs
+++ b/tests/ui/async-await/async-closures/not-fn.rs
@@ -9,7 +9,7 @@ fn main() {
 
     let mut x = 1;
     needs_fn(async || {
-        //~^ ERROR  async closure does not implement `FnMut` because it captures state from its environment
+        //~^ ERROR async closure does not implement `FnMut` because it captures state from its environment
         x += 1;
     });
 }
diff --git a/tests/ui/async-await/async-closures/precise-captures.rs b/tests/ui/async-await/async-closures/precise-captures.rs
index e82dd1dbaf059..c4c67df544fb2 100644
--- a/tests/ui/async-await/async-closures/precise-captures.rs
+++ b/tests/ui/async-await/async-closures/precise-captures.rs
@@ -126,7 +126,7 @@ async fn async_main() {
     {
         let mut s = S { a: 1, b: Drop("drop first"), c: Drop("untouched") };
         let c = guidance!(async move || {
-            // s.a = 2; // FIXME(async_closures): Figure out why this fails
+            s.a = 2;
             drop(s.b);
         });
         s.c.0 = "uncaptured";
@@ -141,7 +141,7 @@ async fn async_main() {
     {
         let mut s = S { a: 1, b: Drop("drop first"), c: Drop("untouched") };
         let c = guidance!(async move || {
-            // s.a = 2; // FIXME(async_closures): Figure out why this fails
+            s.a = 2;
             drop(s.b);
         });
         s.c.0 = "uncaptured";
diff --git a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs
index 18f16ca4b2d30..be3f032b8ff80 100644
--- a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs
+++ b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.rs
@@ -38,10 +38,12 @@ fn through_field_and_ref<'a>(x: &S<'a>) {
     let c = async || { println!("{}", *x.0); }; //~ ERROR `x` does not live long enough
     outlives::<'a>(c());
     outlives::<'a>(call_once(c)); //~ ERROR explicit lifetime required in the type of `x`
+}
 
+fn through_field_and_ref_move<'a>(x: &S<'a>) {
     let c = async move || { println!("{}", *x.0); };
     outlives::<'a>(c()); //~ ERROR `c` does not live long enough
-    // outlives::<'a>(call_once(c)); // FIXME(async_closures): Figure out why this fails
+    outlives::<'a>(call_once(c)); //~ ERROR explicit lifetime required in the type of `x`
 }
 
 fn main() {}
diff --git a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr
index 1df5abdbb18e3..a70aece2dea5f 100644
--- a/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr
+++ b/tests/ui/async-await/async-closures/without-precise-captures-we-are-powerless.stderr
@@ -100,7 +100,6 @@ LL |     let c = async || { println!("{}", *x.0); };
 LL |     outlives::<'a>(c());
 LL |     outlives::<'a>(call_once(c));
    |                    ------------ argument requires that `x` is borrowed for `'a`
-...
 LL | }
    |  - `x` dropped here while still borrowed
 
@@ -114,11 +113,10 @@ LL |     outlives::<'a>(call_once(c));
    |                    ^^^^^^^^^^^^ lifetime `'a` required
 
 error[E0597]: `c` does not live long enough
-  --> $DIR/without-precise-captures-we-are-powerless.rs:43:20
+  --> $DIR/without-precise-captures-we-are-powerless.rs:45:20
    |
-LL | fn through_field_and_ref<'a>(x: &S<'a>) {
-   |                          -- lifetime `'a` defined here
-...
+LL | fn through_field_and_ref_move<'a>(x: &S<'a>) {
+   |                               -- lifetime `'a` defined here
 LL |     let c = async move || { println!("{}", *x.0); };
    |         - binding `c` declared here
 LL |     outlives::<'a>(c());
@@ -126,11 +124,20 @@ LL |     outlives::<'a>(c());
    |                    |
    |                    borrowed value does not live long enough
    |                    argument requires that `c` is borrowed for `'a`
-LL |     // outlives::<'a>(call_once(c)); // FIXME(async_closures): Figure out why this fails
+LL |     outlives::<'a>(call_once(c));
 LL | }
    | - `c` dropped here while still borrowed
 
-error: aborting due to 9 previous errors
+error[E0621]: explicit lifetime required in the type of `x`
+  --> $DIR/without-precise-captures-we-are-powerless.rs:46:20
+   |
+LL | fn through_field_and_ref_move<'a>(x: &S<'a>) {
+   |                                      ------ help: add explicit lifetime `'a` to the type of `x`: `&'a S<'a>`
+...
+LL |     outlives::<'a>(call_once(c));
+   |                    ^^^^^^^^^^^^ lifetime `'a` required
+
+error: aborting due to 10 previous errors
 
 Some errors have detailed explanations: E0505, E0597, E0621.
 For more information about an error, try `rustc --explain E0505`.