diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 2cd5e79..ffb7a64 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -23,6 +23,8 @@ For instance, a test for `buffer.c` must be called `test_buffer.c`.
 There will be no `test_buffer.h`. Instead, `test.c` will directly
 `#include` the C–source-file directly.
 
+Every syntax error path identified in the parser MUST have a corresponding test.
+
 ## Language Syntax
 Since this is a compiler for a new language, do not assume anything
 of its syntax.