diff --git a/src/resolvers/fossil.cr b/src/resolvers/fossil.cr
index 94f6159d..6d67da2d 100644
--- a/src/resolvers/fossil.cr
+++ b/src/resolvers/fossil.cr
@@ -469,7 +469,7 @@ module Shards
       !files.strip.empty?
     end
 
-    private def capture(command, path = local_path)
+    private def capture(command : String, path : String = local_path) : String
       run(command, capture: true, path: path).not_nil!
     end
 
diff --git a/src/resolvers/git.cr b/src/resolvers/git.cr
index 62dd9b93..7ddf5169 100644
--- a/src/resolvers/git.cr
+++ b/src/resolvers/git.cr
@@ -360,7 +360,7 @@ module Shards
       false
     end
 
-    private def origin_url
+    private def origin_url : String
       @origin_url ||= capture("git ls-remote --get-url origin --bare").strip
     end
 
@@ -415,7 +415,7 @@ module Shards
       !files.strip.empty?
     end
 
-    private def capture(command, path = local_path)
+    private def capture(command : String, path : String = local_path) : String
       run(command, capture: true, path: path).not_nil!
     end
 
diff --git a/src/resolvers/hg.cr b/src/resolvers/hg.cr
index f29239ae..c523ecee 100644
--- a/src/resolvers/hg.cr
+++ b/src/resolvers/hg.cr
@@ -379,7 +379,7 @@ module Shards
       File.exists?(File.join(local_path, ".hg", "dirstate"))
     end
 
-    private def origin_url
+    private def origin_url : String
       @origin_url ||= capture("hg paths default").strip
     end
 
@@ -433,7 +433,7 @@ module Shards
       run("hg files -r #{Process.quote(ref.to_hg_revset)} -- #{Process.quote(path)}", raise_on_fail: false)
     end
 
-    private def capture(command, path = local_path)
+    private def capture(command : String, path : String = local_path) : String
       run(command, capture: true, path: path).as(String)
     end