diff --git a/lib/mspec/utils/warnings.rb b/lib/mspec/utils/warnings.rb
index e1964837..1cd9153a 100644
--- a/lib/mspec/utils/warnings.rb
+++ b/lib/mspec/utils/warnings.rb
@@ -1,5 +1,11 @@
 require 'mspec/guards/version'
 
+# Always enable deprecation warnings when running MSpec, as ruby/spec tests for them,
+# and like in most test frameworks, all warnings should be enabled by default (same as -w).
+if Object.const_defined?(:Warning) and Warning.respond_to?(:[]=)
+  Warning[:deprecated] = true
+end
+
 if Object.const_defined?(:Warning) and Warning.respond_to?(:warn)
   def Warning.warn(message)
     # Suppress any warning inside the method to prevent recursion