diff --git a/src/advent/util.cr b/src/advent/util.cr
index 1bcce64..4391232 100644
--- a/src/advent/util.cr
+++ b/src/advent/util.cr
@@ -35,7 +35,7 @@ class Array(T)
   end
 
   def find_indices
-    into = [] of T
+    into = [] of Int32
     each_with_index do |v, i|
       into << i if yield v
     end