diff --git a/lib/gollum.rb b/lib/gollum.rb
index f4b82ca7..21a0c8ea 100644
--- a/lib/gollum.rb
+++ b/lib/gollum.rb
@@ -58,5 +58,19 @@ module Gollum
       'img' => {'href' => ['http', 'https', :relative]}
     }
   }
+
+  class Error < StandardError; end
+  class DuplicatePageError < Error
+    attr_accessor :dir
+    attr_accessor :existing_path
+    attr_accessor :attempted_path
+
+    def initialize(dir, existing, attempted, message = nil)
+      @dir            = dir
+      @existing_path  = existing
+      @attempted_path = attempted
+      super(message || "Cannot write #{@dir}/#{@attempted_path}, found #{@dir}/#{@existing_path}.")
+    end
+  end
 end
 
diff --git a/lib/gollum/wiki.rb b/lib/gollum/wiki.rb
index 49820a59..cd571314 100644
--- a/lib/gollum/wiki.rb
+++ b/lib/gollum/wiki.rb
@@ -315,13 +315,24 @@ module Gollum
       ext  = @page_class.format_to_ext(format)
       path = @page_class.cname(name) + '.' + ext
 
-      parts = dir.split('/')
+      parts     = dir.split('/')
       container = nil
       parts.each do |part|
         container = map[part]
       end
 
-      (container || map)[path] = normalize(data)
+      container ||= map
+      downpath    = path.downcase
+      downpath.sub! /\.\w+$/, ''
+      container.keys.each do |existing|
+        file = existing.downcase
+        file.sub! /\.\w+$/, ''
+        if downpath == file
+          raise DuplicatePageError.new(dir, existing, path)
+        end
+      end
+
+      container[path] = normalize(data)
       map
     end
 
diff --git a/test/test_markup.rb b/test/test_markup.rb
index e56d6851..184d270e 100644
--- a/test/test_markup.rb
+++ b/test/test_markup.rb
@@ -80,15 +80,16 @@ context "Markup" do
   end
 
   test "page link with custom base path" do
-    ["/wiki", "/wiki/"].each do |path|
+    ["/wiki", "/wiki/"].each_with_index do |path, i|
+      name = "Bilbo Baggins #{i}"
       @wiki = Gollum::Wiki.new(@path, :base_path => path)
-      @wiki.write_page("Bilbo Baggins", :markdown, "a [[Bilbo Baggins]] b", @commit)
+      @wiki.write_page(name, :markdown, "a [[#{name}]] b", @commit)
 
-      page = @wiki.page("Bilbo Baggins")
+      page = @wiki.page(name)
       output = page.formatted_data
       assert_match /class="internal present"/,     output
-      assert_match /href="\/wiki\/Bilbo-Baggins"/, output
-      assert_match /\>Bilbo Baggins\</,            output
+      assert_match /href="\/wiki\/Bilbo-Baggins-\d"/, output
+      assert_match /\>Bilbo Baggins \d\</,            output
     end
   end
 
@@ -101,9 +102,10 @@ context "Markup" do
 
   test "image with http url" do
     ['http', 'https'].each do |scheme|
-      @wiki.write_page("Bilbo Baggins", :markdown, "a [[#{scheme}://example.com/bilbo.jpg]] b", @commit)
+      name = "Bilbo Baggins #{scheme}"
+      @wiki.write_page(name, :markdown, "a [[#{scheme}://example.com/bilbo.jpg]] b", @commit)
 
-      page = @wiki.page("Bilbo Baggins")
+      page = @wiki.page(name)
       output = page.formatted_data
       assert_equal %{<p>a <img src="#{scheme}://example.com/bilbo.jpg" /> b</p>}, output
     end
diff --git a/test/test_wiki.rb b/test/test_wiki.rb
index 9ebb5113..f0edfd32 100644
--- a/test/test_wiki.rb
+++ b/test/test_wiki.rb
@@ -95,6 +95,16 @@ context "Wiki page writing" do
     assert @wiki.page("Gollum")
   end
 
+  test "is not allowed to overwrite file" do
+    commit = { :message => "Gollum page",
+               :name => "Tom Preston-Werner",
+               :email => "tom@github.com" }
+    @wiki.write_page("Abc-Def", :markdown, "# Gollum", commit)
+    assert_raises Gollum::DuplicatePageError do
+      @wiki.write_page("ABC DEF", :textile,  "# Gollum", commit)
+    end
+  end
+
   test "update_page" do
     commit = { :message => "Gollum page",
                :name => "Tom Preston-Werner",