diff --git a/README.md b/README.md
index e0b3d50..e7b0a41 100644
--- a/README.md
+++ b/README.md
@@ -46,7 +46,7 @@ See `kitchen_sink.sh` examples.
 
 # Current Status
 
- - [ ] Change message templates to render headers in this order: `author`, `prev`, `lipmaa`, `depth`, `kind`.
+ - [ ] Enforce canonical header ordering: `author`, `prev`, `lipmaa`, `depth`, `kind`.
  - [ ] Change `@`, `%`, `&` to `feed.`, `mesg.`, `blob.`, respectively. Better readability, easier onboarding, URL friendly.
  - [ ] Update Dev docs in protocol spec to reflect changes to `lipmaa` header.
  - [ ] Update spec document CLI usage examples to reflect API changes in 2020.
diff --git a/lib/pigeon.rb b/lib/pigeon.rb
index 45cab7a..418418f 100644
--- a/lib/pigeon.rb
+++ b/lib/pigeon.rb
@@ -13,7 +13,13 @@ module Pigeon
   DEFAULT_BLOB_DIR = File.join(Dir.home, "pigeon_sha256")
   MESSAGE_FILE = "messages.pgn"
   # MESSAGE TEMPLATE CONSTANTS:
-  HEADER_TPL = "author <%= author %>\nkind <%= kind %>\nprev <%= prev %>\ndepth <%= depth %>\nlipmaa <%= lipmaa %>\n\n"
+  HEADER_TPL = [
+    "author <%= author %>",
+    "depth <%= depth %>",
+    "kind <%= kind %>",
+    "lipmaa <%= lipmaa %>\n\n",
+    "prev <%= prev %>",
+  ].join("\n")
   BODY_TPL = "<% body.to_a.each do |k, v| %><%= k %>:<%= v %><%= \"\\n\" %><% end %>\n"
   FOOTER_TPL = "signature <%= signature %>"
   COMPLETE_TPL = [HEADER_TPL, BODY_TPL, FOOTER_TPL].join("")
diff --git a/lib/pigeon/lexer.rb b/lib/pigeon/lexer.rb
index b6f3096..688707f 100644
--- a/lib/pigeon/lexer.rb
+++ b/lib/pigeon/lexer.rb
@@ -94,7 +94,6 @@ module Pigeon
       raise LexError, msg
     end
 
-    # This might be a mistake or uneccessary. NN 20 MAR 2020
     def maybe_end_message!
       if tokens.last.last != :MESSAGE_DELIM
         @tokens << [:MESSAGE_DELIM, scanner.pos]
@@ -102,46 +101,66 @@ module Pigeon
       end
     end
 
+    CANONICAL_ORDERING = {
+      # Current Key => Allowed previous keys
+      AUTHOR: [:FOOTER_SEPERATOR, :START],
+      DEPTH: [:AUTHOR],
+      KIND: [:DEPTH],
+      LIPMAA: [:KIND],
+      PREV: [:LIPMAA],
+      HEADER_SEPERATOR: [:PREV],
+    }
+
+    def check_header_order(current)
+      expected = CANONICAL_ORDERING.fetch(current)
+      if expected.include?(@last_good)
+        @last_good = current
+      else
+        msg = "BAD HEADER ORDERING. Expected: #{expected.join(" OR ")}. Got: #{current}"
+        raise msg
+      end
+    end
+
     def do_header
       if scanner.scan(AUTHOR)
         author = scanner.matched.chomp.gsub("author ", "")
         @tokens << [:AUTHOR, author, scanner.pos]
-        @last_good = :AUTHOR
+        check_header_order(:AUTHOR)
         return
       end
 
       if scanner.scan(DEPTH)
         depth = scanner.matched.chomp.gsub("depth ", "").to_i
         @tokens << [:DEPTH, depth, scanner.pos]
-        @last_good = :DEPTH
+        check_header_order(:DEPTH)
         return
       end
 
       if scanner.scan(LIPMAA)
         depth = scanner.matched.chomp.gsub("lipmaa ", "")
         @tokens << [:LIPMAA, depth, scanner.pos]
-        @last_good = :LIPMAA
+        check_header_order(:LIPMAA)
         return
       end
 
       if scanner.scan(PREV)
         prev = scanner.matched.chomp.gsub("prev ", "")
         @tokens << [:PREV, prev, scanner.pos]
-        @last_good = :PREV
+        check_header_order(:PREV)
         return
       end
 
       if scanner.scan(KIND)
         kind = scanner.matched.chomp.gsub("kind ", "")
         @tokens << [:KIND, kind, scanner.pos]
-        @last_good = :KIND
+        check_header_order(:KIND)
         return
       end
 
       if scanner.scan(SEPERATOR)
         @state = BODY
         @tokens << [:HEADER_END, scanner.pos]
-        @last_good = :HEADER_SEPERATOR
+        check_header_order(:HEADER_SEPERATOR)
         return
       end
 
diff --git a/spec/pigeon/bundle_spec.rb b/spec/pigeon/bundle_spec.rb
index b0d382a..45e684e 100644
--- a/spec/pigeon/bundle_spec.rb
+++ b/spec/pigeon/bundle_spec.rb
@@ -2,7 +2,6 @@ require "spec_helper"
 
 RSpec.describe Pigeon::Message do
   before(:each) do
-    puts "WARNING: This test deletes the blob dir! Fix ASAP"
     `rm -rf #{Pigeon::DEFAULT_BLOB_DIR}`
     p = Pigeon::DEFAULT_BUNDLE_PATH
     File.delete(p) if File.file?(p)