diff --git a/tests/expression/1.0/IExpression.hal b/tests/expression/1.0/IExpression.hal
index a44e03c..6eb5b2a 100644
--- a/tests/expression/1.0/IExpression.hal
+++ b/tests/expression/1.0/IExpression.hal
@@ -178,7 +178,7 @@
     MAX_PLUS_2 // 1
   };
 
-  enum Constants {
+  enum Constants : int32_t {
     CONST_FOO,
     CONST_BAR = 70,
     MAX_ARRAY_SIZE = 20,