diff --git a/src/spectator.cr b/src/spectator.cr
index 81db191..0f23538 100644
--- a/src/spectator.cr
+++ b/src/spectator.cr
@@ -8,6 +8,14 @@ module Spectator
   # Current version of the Spectator library.
   VERSION = {{ `shards version #{__DIR__}`.stringify.chomp }}
 
+  # Inserts code to produce a debug message.
+  # The code will only be injected when `spectator_debug` is defined (`-Dspectator_debug`).
+  macro debug_out(message)
+    {% if flag?(:spectator_debug) %}
+      STDERR.puts {{message}}
+    {% end %}
+  end
+
   # Top-level describe method.
   # All specs in a file must be wrapped in this call.
   # This takes an argument and a block.
diff --git a/src/spectator/spec/builder.cr b/src/spectator/spec/builder.cr
index 0ac3d93..9071b85 100644
--- a/src/spectator/spec/builder.cr
+++ b/src/spectator/spec/builder.cr
@@ -36,9 +36,7 @@ module Spectator
     # The newly created group is returned.
     # It shouldn't be used outside of this class until a matching `#end_group` is called.
     def start_group(name, source = nil) : ExampleGroup
-      {% if flag?(:spectator_debug) %}
-        puts "Start group: #{name.inspect} @ #{source}"
-      {% end %}
+      Spectator.debug_out("Start group: #{name.inspect} @ #{source}")
       ExampleGroup.new(name, source, current_group).tap do |group|
         @group_stack << group
       end
@@ -51,9 +49,7 @@ module Spectator
     # At this point, it is safe to use the group.
     # All of its examples and sub-groups have been populated.
     def end_group : ExampleGroup
-      {% if flag?(:spectator_debug) %}
-        puts "End group: #{current_group}"
-      {% end %}
+      Spectator.debug_out("End group: #{current_group}")
       raise "Can't pop root group" if root?
 
       @group_stack.pop
@@ -78,9 +74,7 @@ module Spectator
     #
     # The newly created example is returned.
     def add_example(name, source, context, &block : Example, Context ->) : Example
-      {% if flag?(:spectator_debug) %}
-        puts "Add example: #{name} @ #{source}"
-      {% end %}
+      Spectator.debug_out("Add example: #{name} @ #{source}")
       delegate = ExampleContextDelegate.new(context, block)
       Example.new(delegate, name, source, current_group)
       # The example is added to the current group by `Example` initializer.