diff --git a/CODECONVENTIONS.md b/CODECONVENTIONS.md
index 78fb912a6a..bceab74618 100644
--- a/CODECONVENTIONS.md
+++ b/CODECONVENTIONS.md
@@ -65,6 +65,10 @@ changes to the correct style.  Without arguments this tool will reformat all
 source code (and may take some time to run).  Otherwise pass as arguments to
 the tool the files that changed and it will only reformat those.
 
+**Important**: Use only [uncrustify](https://github.com/uncrustify/uncrustify)
+v0.71 or v0.72 for MicroPython. Different uncrustify versions produce slightly
+different formatting, and the configuration file formats are often incompatible.
+
 Python code conventions
 =======================
 
diff --git a/tools/uncrustify.cfg b/tools/uncrustify.cfg
index 221fb458e9..28eb49faf7 100644
--- a/tools/uncrustify.cfg
+++ b/tools/uncrustify.cfg
@@ -1,5 +1,8 @@
 # Uncrustify-0.71.0_f
 
+# IMPORTANT: Output is different if using Uncrustify 0.73 or newer, and config file format has changed in newer versions.
+# Use version 0.71 or 0.72 to get matching code formatting.
+
 #
 # General options
 #