diff --git a/LICENSE b/LICENSE
index 244ebdb..7aca136 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2019-2022 Anton Maminov
+Copyright (c) 2019-2023 Anton Maminov
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/shard.yml b/shard.yml
index 04b8edc..1416dd4 100644
--- a/shard.yml
+++ b/shard.yml
@@ -8,6 +8,7 @@ dependencies:
     github: geocrystal/haversine
   convex_hull:
     github: geocrystal/convex_hull
+    version: ">= 0.6.0"
   geohash:
     github: geocrystal/geohash
 
diff --git a/src/geo/coord.cr b/src/geo/coord.cr
index 094fa4b..22c8e16 100644
--- a/src/geo/coord.cr
+++ b/src/geo/coord.cr
@@ -121,12 +121,17 @@ module Geo
     # pos.strfcoord('%latd %latm %0.5lats') # => "0 1 59.99880"
     # pos.strfcoord('%latd %latm %lats')  # => "0 2 0"
     # ```
-    def strfcoord(formatstr)
+    def strfcoord(formatstr) : String
       h = full_hash
 
       DIRECTIVES.reduce(formatstr) do |memo, (from, to)|
         memo.gsub(from) do
-          to = to.call($~) if to.is_a?(Proc)
+          to =
+            if to.is_a?(Proc) && from.is_a?(Regex) && (match_data = memo.match(from))
+              to.call(match_data)
+            else
+              to.as(String)
+            end
 
           res = to % h
 
diff --git a/src/geo/polygon.cr b/src/geo/polygon.cr
index b818563..c711ff4 100644
--- a/src/geo/polygon.cr
+++ b/src/geo/polygon.cr
@@ -128,7 +128,7 @@ module Geo
     private def make_convex_hull(coords : Array(Geo::Coord))
       points = @coords.map { |coord| {coord.lat, coord.lng} }
       convex_hull = ConvexHull::GrahamScan.new(points)
-      hull = convex_hull.convex_hull
+      hull = convex_hull.to_a
 
       hull.map { |point| Geo::Coord.new(point.x.as(Float32 | Float64), point.y.as(Float32 | Float64)) }
     end