diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..156cd51
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,70 @@
+PATH
+  remote: .
+  specs:
+    ronn-ng (0.10.1.pre1)
+      kramdown (~> 2.1)
+      kramdown-parser-gfm (~> 1.0.1)
+      mustache (~> 1.0)
+      nokogiri (~> 1.9, >= 1.9.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ast (2.4.1)
+    kramdown (2.3.1)
+      rexml
+    kramdown-parser-gfm (1.0.1)
+      kramdown (~> 2.0)
+    mini_portile2 (2.4.0)
+    mustache (1.1.1)
+    mustermann (1.1.1)
+      ruby2_keywords (~> 0.0.1)
+    nokogiri (1.10.10)
+      mini_portile2 (~> 2.4.0)
+    parallel (1.20.1)
+    parser (2.7.2.0)
+      ast (~> 2.4.1)
+    power_assert (1.2.0)
+    rack (2.2.3)
+    rack-protection (2.1.0)
+      rack
+    rainbow (3.0.0)
+    rake (12.3.3)
+    regexp_parser (2.0.1)
+    rexml (3.2.5)
+    rubocop (0.93.1)
+      parallel (~> 1.10)
+      parser (>= 2.7.1.5)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8)
+      rexml
+      rubocop-ast (>= 0.6.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 1.4.0, < 2.0)
+    rubocop-ast (1.3.0)
+      parser (>= 2.7.1.5)
+    ruby-progressbar (1.10.1)
+    ruby2_keywords (0.0.2)
+    sinatra (2.1.0)
+      mustermann (~> 1.0)
+      rack (~> 2.2)
+      rack-protection (= 2.1.0)
+      tilt (~> 2.0)
+    test-unit (3.3.7)
+      power_assert
+    tilt (2.0.10)
+    unicode-display_width (1.7.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  rack (~> 2.2, >= 2.2.3)
+  rake (~> 12.3, >= 12.3.3)
+  ronn-ng!
+  rubocop (~> 0.88, >= 0.88.0)
+  sinatra (~> 2.0, >= 2.0.8)
+  test-unit (~> 3.3, >= 3.3.6)
+
+BUNDLED WITH
+   2.1.4
diff --git a/lib/ronn/document.rb b/lib/ronn/document.rb
index 9a25373..15bef2c 100644
--- a/lib/ronn/document.rb
+++ b/lib/ronn/document.rb
@@ -179,11 +179,14 @@ def title
     end
 
     # The date the man page was published. If not set explicitly,
-    # this is the file's modified time or, if no file is given,
+    # it first checks for "SOURCE_DATE_EPOCH" to support reproducible
+    # builds, then the file's modified time or, if no file is given,
     # the current time. Center displayed in the document footer.
     def date
       return @date if @date
 
+      return Time.at(ENV['SOURCE_DATE_EPOCH'].to_i).gmtime if ENV['SOURCE_DATE_EPOCH']
+
       return File.mtime(path) if File.exist?(path)
 
       Time.now