diff --git a/Gemfile b/Gemfile
index e7d733d..f68557e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,4 +5,7 @@ gemspec
 group :development do
   gem 'rake',                 :platforms => :ruby_18
 end
-                  
+
+group :debugger do
+  gem 'pry-debugger'
+end
diff --git a/Gemfile.lock b/Gemfile.lock
index 56af75c..3281d8a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,10 +1,10 @@
 PATH
   remote: .
   specs:
-    swissmedic-diff (0.1.5)
+    swissmedic-diff (0.1.6)
       nokogiri
       rubyXL
-      rubyzip
+      rubyzip (= 0.9.9)
       spreadsheet
 
 GEM
@@ -12,9 +12,18 @@ GEM
   specs:
     ansi (1.4.3)
     builder (3.2.2)
+    coderay (1.1.0)
+    columnize (0.3.6)
+    debugger (1.6.5)
+      columnize (>= 0.3.1)
+      debugger-linecache (~> 1.2.0)
+      debugger-ruby_core_source (~> 1.3.1)
+    debugger-linecache (1.2.0)
+    debugger-ruby_core_source (1.3.1)
     hashie (2.0.5)
     hoe (3.7.4)
       rake (>= 0.8, < 11.0)
+    method_source (0.8.2)
     mini_portile (0.5.2)
     minitest (5.2.1)
     minitest-reporters (1.0.0)
@@ -27,10 +36,18 @@ GEM
     powerbar (1.0.11)
       ansi (~> 1.4.0)
       hashie (>= 1.1.0)
+    pry (0.9.12.4)
+      coderay (~> 1.0)
+      method_source (~> 0.8)
+      slop (~> 3.4)
+    pry-debugger (0.2.2)
+      debugger (~> 1.3)
+      pry (~> 0.9.10)
     rake (10.1.1)
     ruby-ole (1.2.11.7)
     rubyXL (1.2.10)
     rubyzip (0.9.9)
+    slop (3.4.7)
     spreadsheet (0.9.6)
       ruby-ole (>= 1.0)
 
@@ -41,5 +58,6 @@ DEPENDENCIES
   hoe
   minitest
   minitest-reporters
+  pry-debugger
   rake
   swissmedic-diff!