diff --git a/ext/json/lib/json/common.rb b/ext/json/lib/json/common.rb
index 8f34f1f05a..37427534e0 100644
--- a/ext/json/lib/json/common.rb
+++ b/ext/json/lib/json/common.rb
@@ -1005,6 +1005,12 @@ module ::Kernel
   # Outputs _objs_ to STDOUT as JSON strings in the shortest form, that is in
   # one line.
   def j(*objs)
+    if RUBY_VERSION >= "3.0"
+      warn "Kernel#j is deprecated and will be removed in json 3.0.0", uplevel: 1, category: :deprecated
+    else
+      warn "Kernel#j is deprecated and will be removed in json 3.0.0", uplevel: 1
+    end
+
     objs.each do |obj|
       puts JSON::generate(obj, :allow_nan => true, :max_nesting => false)
     end
@@ -1014,6 +1020,12 @@ module ::Kernel
   # Outputs _objs_ to STDOUT as JSON strings in a pretty format, with
   # indentation and over many lines.
   def jj(*objs)
+    if RUBY_VERSION >= "3.0"
+      warn "Kernel#jj is deprecated and will be removed in json 3.0.0", uplevel: 1, category: :deprecated
+    else
+      warn "Kernel#jj is deprecated and will be removed in json 3.0.0", uplevel: 1
+    end
+
     objs.each do |obj|
       puts JSON::pretty_generate(obj, :allow_nan => true, :max_nesting => false)
     end