diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index 86e1ac1e65..06c3adc0a1 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -669,6 +669,10 @@ typedef struct ExprEvalStep
 	}			d;
 } ExprEvalStep;
 
+/* Enforce the size rule given in the comment above */
+StaticAssertDecl(sizeof(ExprEvalStep) <= 64,
+				 "size of ExprEvalStep exceeds 64 bytes");
+
 
 /* Non-inline data for container operations */
 typedef struct SubscriptingRefState