diff --git a/lib/squib/api/text_embed.rb b/lib/squib/api/text_embed.rb
index 20e3b05..073e96c 100644
--- a/lib/squib/api/text_embed.rb
+++ b/lib/squib/api/text_embed.rb
@@ -37,7 +37,7 @@ module Squib
     # @option opts angle [FixNum] (0) Rotation of the in radians. Note that this rotates around the upper-left corner, making the placement of x-y coordinates slightly tricky. Supports Arrays, see {file:README.md#Arrays_and_Singleton_Expansion Arrays and Singleon Expansion}
     # @api public
     def svg(opts = {})
-      # TODO: add input validation for key here
+      key   = Args::EmbedKey.new.validate_key(opts[:key])
       range = Args::CardRange.new(opts[:range], deck_size: @deck_size)
       paint = Args::Paint.new(@custom_colors).load!(opts, expand_by: @deck_size, layout: @layout)
       box   = Args::Box.new(self, {width: :native, height: :native}).load!(opts, expand_by: @deck_size, layout: @layout, dpi: @dpi)
@@ -52,7 +52,7 @@ module Squib
         b.x, b.y = x, y
         card.svg(ifile[i].file, svg_args[i], b, paint[i], trans[i])
       end
-      @rules[opts[:key]] = rule
+      @rules[key] = rule
     end
 
     # Context object for embedding a png within text
@@ -69,7 +69,7 @@ module Squib
     # @option opts angle [FixNum] (0) Rotation of the in radians. Note that this rotates around the upper-left corner, making the placement of x-y coordinates slightly tricky. Supports Arrays, see {file:README.md#Arrays_and_Singleton_Expansion Arrays and Singleon Expansion}
     # @api public
     def png(opts = {})
-      # TODO: add input validation for key here
+      key   = Args::EmbedKey.new.validate_key(opts[:key])
       range = Args::CardRange.new(opts[:range], deck_size: @deck_size)
       paint = Args::Paint.new(@custom_colors).load!(opts, expand_by: @deck_size, layout: @layout)
       box   = Args::Box.new(self, {width: :native, height: :native}).load!(opts, expand_by: @deck_size, layout: @layout, dpi: @dpi)
@@ -83,7 +83,7 @@ module Squib
         b.x, b.y = x, y
         card.png(ifile[i].file, b, paint[i], trans[i])
       end
-      @rules[opts[:key]] = rule
+      @rules[key] = rule
     end
 
   end
diff --git a/lib/squib/args/embed_key.rb b/lib/squib/args/embed_key.rb
new file mode 100644
index 0000000..347b246
--- /dev/null
+++ b/lib/squib/args/embed_key.rb
@@ -0,0 +1,17 @@
+require 'squib/args/arg_loader'
+
+module Squib
+  # @api private
+  module Args
+
+    class EmbedKey
+
+      # Validate the embed lookup key
+      def validate_key(str)
+        str.to_s
+      end
+
+    end
+
+  end
+end
diff --git a/spec/args/embed_key_spec.rb b/spec/args/embed_key_spec.rb
new file mode 100644
index 0000000..6b81206
--- /dev/null
+++ b/spec/args/embed_key_spec.rb
@@ -0,0 +1,13 @@
+require 'spec_helper'
+require 'squib/args/embed_key'
+
+describe Squib::Args::EmbedKey do
+
+  context '#validate_key' do
+
+    it 'converts to string' do
+      expect(subject.validate_key(2.5)).to eq ('2.5')
+    end
+
+  end
+end