diff --git a/packages/casl-ability/src/extra.ts b/packages/casl-ability/src/extra.ts
index f96a425ee..9db2e8de1 100644
--- a/packages/casl-ability/src/extra.ts
+++ b/packages/casl-ability/src/extra.ts
@@ -94,14 +94,13 @@ export function permittedFieldsOf(
 
 const joinIfArray = (value: string | string[]) => Array.isArray(value) ? value.join(',') : value;
 
-export type PackedRule = [
-  string,
-  string,
-  (UnifiedRawRule['conditions'] | 0)?,
-  (1 | 0)?,
-  (string | 0)?,
-  (string | 0)?
-];
+export type PackedRule =
+  [string, string] |
+  [string, string, UnifiedRawRule['conditions']] |
+  [string, string, UnifiedRawRule['conditions'] | 0, 1] |
+  [string, string, UnifiedRawRule['conditions'] | 0, 1 | 0, string] |
+  [string, string, UnifiedRawRule['conditions'] | 0, 1 | 0, string | 0, string]
+;
 
 export function packRules(rules: UnifiedRawRule[]): PackedRule[] {
   return rules.map(({ actions, subject, conditions, inverted, fields, reason }) => { // eslint-disable-line
@@ -111,7 +110,7 @@ export function packRules(rules: UnifiedRawRule[]): PackedRule[] {
       conditions || 0,
       inverted ? 1 : 0,
       fields ? joinIfArray(fields) : 0,
-      reason || 0
+      reason || ''
     ];
 
     while (!rule[rule.length - 1]) rule.pop();