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diff --git a/compiler/rustc_error_codes/src/error_codes/E0594.md b/compiler/rustc_error_codes/src/error_codes/E0594.md
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+A non-mutable value was assigned a value.
+
+Erroneous code example:
+
+```compile_fail,E0594
+struct SolarSystem {
+    earth: i32,
+}
+
+let ss = SolarSystem { earth: 3 };
+ss.earth = 2; // error!
+```
+
+To fix this error, declare `ss` as mutable by using the `mut` keyword:
+
+```
+struct SolarSystem {
+    earth: i32,
+}
+
+let mut ss = SolarSystem { earth: 3 }; // declaring `ss` as mutable
+ss.earth = 2; // ok!
+```