2 files changed, 28 insertions, 1 deletions
diff --git a/src/librustc_error_codes/error_codes.rs b/src/librustc_error_codes/error_codes.rs
index 7f111b42403..9e4b704170b 100644
--- a/src/librustc_error_codes/error_codes.rs
+++ b/src/librustc_error_codes/error_codes.rs
@@ -347,6 +347,7 @@ E0622: include_str!("./error_codes/E0622.md"),
 E0623: include_str!("./error_codes/E0623.md"),
 E0624: include_str!("./error_codes/E0624.md"),
 E0626: include_str!("./error_codes/E0626.md"),
+E0631: include_str!("./error_codes/E0631.md"),
 E0633: include_str!("./error_codes/E0633.md"),
 E0635: include_str!("./error_codes/E0635.md"),
 E0636: include_str!("./error_codes/E0636.md"),
@@ -580,7 +581,6 @@ E0745: include_str!("./error_codes/E0745.md"),
     // rustc_const_unstable attribute must be paired with stable/unstable
     // attribute
     E0630,
-    E0631, // type mismatch in closure arguments
     E0632, // cannot provide explicit generic arguments when `impl Trait` is
            // used in argument position
     E0634, // type has conflicting packed representaton hints
diff --git a/src/librustc_error_codes/error_codes/E0631.md b/src/librustc_error_codes/error_codes/E0631.md
new file mode 100644
index 00000000000..6188d5f61a7
--- /dev/null
+++ b/src/librustc_error_codes/error_codes/E0631.md
@@ -0,0 +1,27 @@
+This error indicates a type mismatch in closure arguments.
+
+Erroneous code example:
+
+```compile_fail,E0631
+fn foo<F: Fn(i32)>(f: F) {
+}
+
+fn main() {
+    foo(|x: &str| {});
+}
+```
+
+The error occurs because `foo` accepts a closure that takes an `i32` argument,
+but in `main`, it is passed a closure with a `&str` argument.
+
+This can be resolved by changing the type annotation or removing it entirely
+if it can be inferred.
+
+```
+fn foo<F: Fn(i32)>(f: F) {
+}
+
+fn main() {
+    foo(|x: i32| {});
+}
+```