diff --git a/changelog.md b/changelog.md
index 665346ad70..f37565fcbc 100644
--- a/changelog.md
+++ b/changelog.md
@@ -35,6 +35,10 @@ errors.
 
 - Adds a new warning `--warning:ImplicitRangeConversion` that detects downsizing implicit conversions to range types (e.g., `int -> range[0..255]` or `range[1..256] -> range[0..255]`) that could cause runtime panics. Safe conversions like `range[0..255] -> range[0..65535]` and explicit casts do not trigger warnings. `int` to `Natural` and `Positive` conversions do not trigger warnings, which can be enabled with `--warning:systemRangeConversion`.
 
+- Procedure compatibility also checks the backend representation of the
+parameter and result types, not just their source-level shape. Use
+`--legacy:procParamTypeBackendAliases` to restore the older behavior.
+
 ## Standard library additions and changes
 
 [//]: # "Additions:"
diff --git a/doc/manual.md b/doc/manual.md
index ab06f7aa4b..40897ac108 100644
--- a/doc/manual.md
+++ b/doc/manual.md
@@ -1024,6 +1024,9 @@ These are the major type classes:
 * procedural type
 * generic type
 
+The compiler's internal type zoo is richer than this summary suggests:
+some types that are structurally equal still differ in backend representation.
+
 
 Ordinal types
 -------------
@@ -2174,6 +2177,10 @@ Procedural type
 A procedural type is internally a pointer to a procedure. `nil` is
 an allowed value for a variable of a procedural type.
 
+Procedure compatibility also checks the backend representation of the
+parameter and result types, not just their source-level shape. Use
+`--legacy:procParamTypeBackendAliases` to restore the older behavior.
+
 Examples:
 
   ```nim