diff --git a/lib/permissions/special-roles.js b/lib/permissions/special-roles.js
--- a/lib/permissions/special-roles.js
+++ b/lib/permissions/special-roles.js
@@ -18,7 +18,7 @@
 });
 
 export type SpecialRole = $Values<typeof specialRoles>;
-export const specialRoleValidator: TRefinement<number> = tNumEnum(
+export const specialRoleValidator: TRefinement<SpecialRole> = tNumEnum(
   values(specialRoles),
 );
 
diff --git a/lib/types/relationship-types.js b/lib/types/relationship-types.js
--- a/lib/types/relationship-types.js
+++ b/lib/types/relationship-types.js
@@ -33,9 +33,8 @@
   BOTH_BLOCKED: 6,
 });
 export type UserRelationshipStatus = $Values<typeof userRelationshipStatus>;
-export const userRelationshipStatusValidator: TRefinement<number> = tNumEnum(
-  values(userRelationshipStatus),
-);
+export const userRelationshipStatusValidator: TRefinement<UserRelationshipStatus> =
+  tNumEnum(values(userRelationshipStatus));
 
 const traditionalRelationshipActions = Object.freeze({
   FRIEND: 'friend',
diff --git a/lib/types/thread-types-enum.js b/lib/types/thread-types-enum.js
--- a/lib/types/thread-types-enum.js
+++ b/lib/types/thread-types-enum.js
@@ -99,7 +99,7 @@
   return threadType;
 }
 
-export const thinThreadTypeValidator: TRefinement<number> = tNumEnum(
+export const thinThreadTypeValidator: TRefinement<ThinThreadType> = tNumEnum(
   values(thinThreadTypes),
 );
 
@@ -113,7 +113,8 @@
   );
   return threadType;
 }
-export const thickThreadTypeValidator: TRefinement<number> = tNumEnum(
+
+export const thickThreadTypeValidator: TRefinement<ThickThreadType> = tNumEnum(
   values(thickThreadTypes),
 );
 
@@ -153,6 +154,6 @@
   return threadType;
 }
 
-export const threadTypeValidator: TRefinement<number> = tNumEnum(
+export const threadTypeValidator: TRefinement<ThreadType> = tNumEnum(
   values(threadTypes),
 );
diff --git a/lib/utils/validation-utils.js b/lib/utils/validation-utils.js
--- a/lib/utils/validation-utils.js
+++ b/lib/utils/validation-utils.js
@@ -51,8 +51,12 @@
   return t.refinement(t.String, val => regex.test(val));
 }
 
-function tNumEnum(nums: $ReadOnlyArray<number>): TRefinement<number> {
-  return t.refinement(t.Number, (input: number) => {
+function tNumEnum<T: number>(nums: $ReadOnlyArray<T>): TRefinement<T> {
+  const baseType: TIrreducible<T> = t.irreducible<T>(
+    'number',
+    x => typeof x === 'number' && isFinite(x) && !isNaN(x),
+  );
+  return t.refinement(baseType, (input: T) => {
     for (const num of nums) {
       if (input === num) {
         return true;
@@ -61,6 +65,7 @@
     return false;
   });
 }
+
 const tNull: TIrreducible<null> = t.irreducible('null', x => x === null);
 const tDate: TRegex = tRegex(/^[0-9]{4}-[0-1][0-9]-[0-3][0-9]$/);
 const tColor: TRegex = tRegex(validHexColorRegex); // we don't include # char