diff --git a/src/spectator.cr b/src/spectator.cr
index 3dff022..88238a8 100644
--- a/src/spectator.cr
+++ b/src/spectator.cr
@@ -50,7 +50,7 @@ module Spectator
   # A `ConfigBuilder` is yielded to allow changing the configuration.
   # NOTE: The configuration set here can be overriden
   # with a `.spectator` file and command-line arguments.
-  def configure : Nil
+  def configure(& : ConfigBuilder -> _) : Nil
     yield @@config_builder
   end
 
diff --git a/src/spectator/spec/builder.cr b/src/spectator/spec/builder.cr
index f9a4ced..63975c4 100644
--- a/src/spectator/spec/builder.cr
+++ b/src/spectator/spec/builder.cr
@@ -175,7 +175,7 @@ module Spectator
       # Builds the configuration to use for the spec.
       # A `ConfigBuilder` is yielded to the block provided to this method.
       # That builder will be used to create the configuration.
-      def config
+      def configure(& : ConfigBuilder -> _) : Nil
         builder = ConfigBuilder.new
         yield builder
         @config = builder.build