diff --git a/gem2rpm.yml b/gem2rpm.yml
index cc54bd0..ec7ae68 100644
--- a/gem2rpm.yml
+++ b/gem2rpm.yml
@@ -3,3 +3,5 @@
   Ronn builds manuals. It converts simple, human readable textfiles to roff
   for terminal display, and also to HTML for the web.
 :license: MIT
+:patches:
+   ronn-date.patch: -p1
diff --git a/ronn-date.patch b/ronn-date.patch
new file mode 100644
index 0000000..4a865ce
--- /dev/null
+++ b/ronn-date.patch
@@ -0,0 +1,29 @@
+https://github.com/kamontat/ronn/pull/3
+originally based on https://github.com/rtomayko/ronn/pull/98
+
+commit 206846900163c8a538437444dfdd67a7a81e3801
+Author: Bernhard M. Wiedemann <bwiedemann@suse.de>
+Date:   Mon Dec 9 14:36:21 2019 +0100
+
+    Allow to override build date with SOURCE_DATE_EPOCH
+    
+    in order to make builds reproducible.
+    See https://reproducible-builds.org/ for why this is good
+    and https://reproducible-builds.org/specs/source-date-epoch/
+    for the definition of this variable.
+    
+    It prioritizes the variable over mtime
+    because openSUSE's `tallow` package touched a .md file with a patch.
+
+diff --git a/lib/ronn/document.rb b/lib/ronn/document.rb
+index d42e2f9..6590c92 100644
+--- a/lib/ronn/document.rb
++++ b/lib/ronn/document.rb
+@@ -171,6 +171,7 @@ module Ronn
+     # the current time.
+     def date
+       return @date if @date
++      return Time.at(ENV['SOURCE_DATE_EPOCH'].to_i).gmtime if not ENV['SOURCE_DATE_EPOCH'].nil?
+       return File.mtime(path) if File.exist?(path)
+       Time.now
+     end
diff --git a/rubygem-ronn.changes b/rubygem-ronn.changes
index dbaf067..bb243e2 100644
--- a/rubygem-ronn.changes
+++ b/rubygem-ronn.changes
@@ -1,3 +1,8 @@
+-------------------------------------------------------------------
+Mon Dec  9 10:26:45 UTC 2019 - Bernhard Wiedemann <bwiedemann@suse.com>
+
+- Add ronn-date.patch to have reprodubible build time (boo#1047218)
+
 -------------------------------------------------------------------
 Tue Apr 25 17:12:12 UTC 2017 - avvissu@yandex.by
 
diff --git a/rubygem-ronn.spec b/rubygem-ronn.spec
index dafb796..dbc78da 100644
--- a/rubygem-ronn.spec
+++ b/rubygem-ronn.spec
@@ -1,7 +1,7 @@
 #
 # spec file for package rubygem-ronn
 #
-# Copyright (c) 2018 SUSE LINUX GmbH, Nuernberg, Germany.
+# Copyright (c) 2019 SUSE LINUX GmbH, Nuernberg, Germany.
 #
 # All modifications and additions to the file contributed by third parties
 # remain the property of their copyright owners, unless otherwise agreed
@@ -37,6 +37,9 @@ BuildRequires:  update-alternatives
 Url:            http://rtomayko.github.com/ronn
 Source:         https://rubygems.org/gems/%{mod_full_name}.gem
 Source1:        gem2rpm.yml
+# MANUAL
+Patch0:  ronn-date.patch
+# /MANUAL
 Summary:        Builds manuals
 License:        MIT
 Group:          Development/Languages/Ruby
@@ -47,6 +50,10 @@ Ronn builds manuals. It converts simple, human readable textfiles to roff
 for terminal display, and also to HTML for the web.
 
 %prep
+%gem_unpack
+%patch0 -p1
+find -type f -print0 | xargs -0 touch -r %{S:0}
+%gem_build
 
 %build