diff --git a/CHANGELOG.md b/CHANGELOG.md
index 30517382..61fe4bd9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,9 @@
 
 * Added `init_rw_memory` module for cartridge targets.
 
+* **Breaking change!** Preinitialized writable arrays on cartridge targets
+can no longer be read before an explicit call to `init_rw_memory`, either add the call or make the arrays const.
+
 * Added `ensure_mixedcase` function and `oldpet` and `origpet` text encodings.
 
 * Added `MILLFORK_VERSION` preprocessor parameter.
diff --git a/docs/lang/syntax.md b/docs/lang/syntax.md
index 4e033588..ce1d02df 100644
--- a/docs/lang/syntax.md
+++ b/docs/lang/syntax.md
@@ -116,7 +116,11 @@ Syntax:
 then defaults to `default_code_segment` as defined for the platform if the array has initial values,
 or to `default` if it doesn't.
 
-* if `const` is present, the array is read-only. Read-only arrays have to have a fixed address and/or defined contents.
+* if `const` is present, the array is read-only. Read-only arrays have to have a fixed address and/or defined contents.  
+**COMPATIBILITY WARNING!** In Millfork 0.3.2 and earlier, arrays couldn't be declared const and on cartridge-based targets,
+preinitialized arrays were assumed to be immutable and were allocated to ROM.
+Since 0.3.4, only const arrays can be allocated to ROM, non-const arrays are allocated to RAM
+and their contents are uninitialized before a call to `init_rw_memory`. See [the ROM vs RAM guide](../api/rom-vs-ram.md).
 
 * `<element type>`: type of the elements of the array.
 It must be of size 1 byte.