diff --git a/compiler/rustc_hir_typeck/src/check.rs b/compiler/rustc_hir_typeck/src/check.rs
index 69ccbf0b58f..0a1b639af51 100644
--- a/compiler/rustc_hir_typeck/src/check.rs
+++ b/compiler/rustc_hir_typeck/src/check.rs
@@ -92,10 +92,7 @@ pub(super) fn check_fn<'a, 'tcx>(
         fcx.check_pat_top(&param.pat, param_ty, ty_span, None);
 
         // Check that argument is Sized.
-        // The check for a non-trivial pattern is a hack to avoid duplicate warnings
-        // for simple cases like `fn foo(x: Trait)`,
-        // where we would error once on the parameter as a whole, and once on the binding `x`.
-        if param.pat.simple_ident().is_none() && !params_can_be_unsized {
+        if !params_can_be_unsized {
             fcx.require_type_is_sized(
                 param_ty,
                 param.pat.span,
diff --git a/tests/ui/closures/cannot-call-unsized-via-ptr-2.rs b/tests/ui/closures/cannot-call-unsized-via-ptr-2.rs
new file mode 100644
index 00000000000..2d8565517e8
--- /dev/null
+++ b/tests/ui/closures/cannot-call-unsized-via-ptr-2.rs
@@ -0,0 +1,11 @@
+#![feature(unsized_fn_params)]
+
+fn main() {
+    // CoerceMany "LUB"
+    let f = if true { |_a| {} } else { |_b| {} };
+    //~^ ERROR the size for values of type `[u8]` cannot be known at compilation time
+    //~| ERROR the size for values of type `[u8]` cannot be known at compilation time
+
+    let slice: Box<[u8]> = Box::new([1; 8]);
+    f(*slice);
+}
diff --git a/tests/ui/closures/cannot-call-unsized-via-ptr-2.stderr b/tests/ui/closures/cannot-call-unsized-via-ptr-2.stderr
new file mode 100644
index 00000000000..d88b84365df
--- /dev/null
+++ b/tests/ui/closures/cannot-call-unsized-via-ptr-2.stderr
@@ -0,0 +1,21 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> $DIR/cannot-call-unsized-via-ptr-2.rs:5:24
+   |
+LL |     let f = if true { |_a| {} } else { |_b| {} };
+   |                        ^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> $DIR/cannot-call-unsized-via-ptr-2.rs:5:41
+   |
+LL |     let f = if true { |_a| {} } else { |_b| {} };
+   |                                         ^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/closures/cannot-call-unsized-via-ptr.rs b/tests/ui/closures/cannot-call-unsized-via-ptr.rs
new file mode 100644
index 00000000000..5ce4650b033
--- /dev/null
+++ b/tests/ui/closures/cannot-call-unsized-via-ptr.rs
@@ -0,0 +1,10 @@
+#![feature(unsized_fn_params)]
+
+fn main() {
+    // Simple coercion
+    let f: fn([u8]) = |_result| {};
+    //~^ ERROR the size for values of type `[u8]` cannot be known at compilation time
+
+    let slice: Box<[u8]> = Box::new([1; 8]);
+    f(*slice);
+}
diff --git a/tests/ui/closures/cannot-call-unsized-via-ptr.stderr b/tests/ui/closures/cannot-call-unsized-via-ptr.stderr
new file mode 100644
index 00000000000..9ecc66d5ce8
--- /dev/null
+++ b/tests/ui/closures/cannot-call-unsized-via-ptr.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> $DIR/cannot-call-unsized-via-ptr.rs:5:24
+   |
+LL |     let f: fn([u8]) = |_result| {};
+   |                        ^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/issues/issue-5883.rs b/tests/ui/issues/issue-5883.rs
index 82866b35557..f9dd2c54d99 100644
--- a/tests/ui/issues/issue-5883.rs
+++ b/tests/ui/issues/issue-5883.rs
@@ -6,7 +6,7 @@ struct Struct {
 
 fn new_struct(
     r: dyn A + 'static //~ ERROR the size for values of type
-) -> Struct {          //~ ERROR the size for values of type
+) -> Struct {
     Struct { r: r }
 }
 
diff --git a/tests/ui/issues/issue-5883.stderr b/tests/ui/issues/issue-5883.stderr
index ffff403e0d4..a3e2531b5ca 100644
--- a/tests/ui/issues/issue-5883.stderr
+++ b/tests/ui/issues/issue-5883.stderr
@@ -15,22 +15,6 @@ help: function arguments must have a statically known size, borrowed types alway
 LL |     r: &dyn A + 'static
    |        +
 
-error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
-  --> $DIR/issue-5883.rs:9:6
-   |
-LL | ) -> Struct {
-   |      ^^^^^^ doesn't have a size known at compile-time
-LL |     Struct { r: r }
-   |     --------------- this returned value is of type `Struct`
-   |
-   = help: within `Struct`, the trait `Sized` is not implemented for `(dyn A + 'static)`
-note: required because it appears within the type `Struct`
-  --> $DIR/issue-5883.rs:3:8
-   |
-LL | struct Struct {
-   |        ^^^^^^
-   = note: the return type of a function must have a statically known size
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0277`.