diff --git a/tests/baz/1.0/IBase.hal b/tests/baz/1.0/IBase.hal
index add415343d..7f90f16f2a 100644
--- a/tests/baz/1.0/IBase.hal
+++ b/tests/baz/1.0/IBase.hal
@@ -17,7 +17,7 @@
 package android.hardware.tests.baz@1.0;
 
 interface IBase {
-    enum SomeBaseEnum {
+    enum SomeBaseEnum : int32_t {
         grrr = 1,
     };
 
diff --git a/tests/expression/1.0/IExpression.hal b/tests/expression/1.0/IExpression.hal
index a44e03c151..6eb5b2a4b7 100644
--- a/tests/expression/1.0/IExpression.hal
+++ b/tests/expression/1.0/IExpression.hal
@@ -178,7 +178,7 @@ interface IExpression {
     MAX_PLUS_2 // 1
   };
 
-  enum Constants {
+  enum Constants : int32_t {
     CONST_FOO,
     CONST_BAR = 70,
     MAX_ARRAY_SIZE = 20,
diff --git a/wifi/1.0/types.hal b/wifi/1.0/types.hal
index 066662c1f9..9e53377c2e 100644
--- a/wifi/1.0/types.hal
+++ b/wifi/1.0/types.hal
@@ -486,7 +486,7 @@ struct StaScanResult {
 /**
  * Mask of flags set in the |ScanData| instance.
  */
-enum StaScanDataFlagMask {
+enum StaScanDataFlagMask : int32_t {
   /**
    * Indicates that a scan was interrupted/did not occur so results may be
    * incomplete.