diff --git a/.travis.yml b/.travis.yml
index 34bafb0..d10a2ee 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,6 +4,7 @@ cache: bundler
 
 matrix:
   include:
+    - rvm: 2.3
     - rvm: 2.4
     - rvm: 2.5
     - rvm: 2.6
diff --git a/lib/protocol/http2/frame.rb b/lib/protocol/http2/frame.rb
index 1e6ab3c..2f8307b 100644
--- a/lib/protocol/http2/frame.rb
+++ b/lib/protocol/http2/frame.rb
@@ -20,6 +20,7 @@
 # THE SOFTWARE.
 
 require_relative 'error'
+require_relative 'monkey_patch'
 
 module Protocol
 	module HTTP2
diff --git a/lib/protocol/http2/monkey_patch.rb b/lib/protocol/http2/monkey_patch.rb
new file mode 100644
index 0000000..058460b
--- /dev/null
+++ b/lib/protocol/http2/monkey_patch.rb
@@ -0,0 +1,10 @@
+begin
+  ''.unpack1('*')
+rescue => NoMethodError
+  # for compat ruby 2.3
+  class String
+    def unpack1(template)
+      unpack(template).first
+    end
+  end
+end