diff --git a/Tools/cases_generator/interpreter_definition.md b/Tools/cases_generator/interpreter_definition.md
index 1ee4306f3eac1d..72020133738fa5 100644
--- a/Tools/cases_generator/interpreter_definition.md
+++ b/Tools/cases_generator/interpreter_definition.md
@@ -81,7 +81,7 @@ and a piece of C code describing its semantics:
     (definition | family | pseudo)+
 
   definition:
-    "inst" "(" NAME ["," stack_effect] ")" "{" C-code "}"
+    "inst" "(" NAME "," stack_effect ")" "{" C-code "}"
     |
     "op" "(" NAME "," stack_effect ")" "{" C-code "}"
     |