diff --git a/lib/redmine/plugin.rb b/lib/redmine/plugin.rb
index 30c182d..0a95fee 100644
--- a/lib/redmine/plugin.rb
+++ b/lib/redmine/plugin.rb
@@ -158,7 +158,9 @@ module Redmine #:nodoc:
     end
 
     # Sets a requirement on Redmine version
-    # Raises a PluginRequirementError exception if the requirement is not met
+    # Raises a PluginRequirementError exception if the requirement is not met.
+    # if the current branch is 'devel' -- that is, the user is on Redmine
+    # trunk, print a warning instead.
     #
     # Examples
     #   # Requires Redmine 0.7.3 or higher
@@ -186,17 +188,17 @@ module Redmine #:nodoc:
         when :version_or_higher
           raise ArgumentError.new(":version_or_higher accepts a version string only") unless req.is_a?(String)
           unless compare_versions(req, current) <= 0
-            raise PluginRequirementError.new("#{id} plugin requires Redmine #{req} or higher but current is #{current.join('.')}")
+            plugin_version_mismatch("#{id} plugin requires Redmine #{req} or higher but current is #{current.join('.')}")
           end
         when :version
           req = [req] if req.is_a?(String)
           if req.is_a?(Array)
             unless req.detect {|ver| compare_versions(ver, current) == 0}
-              raise PluginRequirementError.new("#{id} plugin requires one the following Redmine versions: #{req.join(', ')} but current is #{current.join('.')}")
+              plugin_version_mismatch("#{id} plugin requires one the following Redmine versions: #{req.join(', ')} but current is #{current.join('.')}")
             end
           elsif req.is_a?(Range)
             unless compare_versions(req.first, current) <= 0 && compare_versions(req.last, current) >= 0
-              raise PluginRequirementError.new("#{id} plugin requires a Redmine version between #{req.first} and #{req.last} but current is #{current.join('.')}")
+              plugin_version_mismatch("#{id} plugin requires a Redmine version between #{req.first} and #{req.last} but current is #{current.join('.')}")
             end
           else
             raise ArgumentError.new(":version option accepts a version string, an array or a range of versions")
@@ -206,6 +208,16 @@ module Redmine #:nodoc:
       true
     end
 
+    def plugin_version_mismatch(message)
+      if Redmine::VERSION.to_a[3] == 'devel'
+        warn "warning: #{message}"
+        warn "warning: this would have caused an abort if you weren't on trunk"
+      else
+        raise PluginRequirementError.new(message)
+      end
+    end
+    private :plugin_version_mismatch
+
     def compare_versions(requirement, current)
       requirement = requirement.split('.').collect(&:to_i)
       requirement <=> current.slice(0, requirement.size)
diff --git a/test/unit/lib/redmine/plugin_test.rb b/test/unit/lib/redmine/plugin_test.rb
index ecf0546..d68cefa 100644
--- a/test/unit/lib/redmine/plugin_test.rb
+++ b/test/unit/lib/redmine/plugin_test.rb
@@ -133,6 +133,13 @@ class Redmine::PluginTest < ActiveSupport::TestCase
     assert_raise Redmine::PluginRequirementError do
       plugin.requires_redmine(:version_or_higher => '2.2')
     end
+
+    # Warn instead of failing if branch is 'devel'
+    Redmine::VERSION.stubs(:to_a).returns([2, 1, 3, "devel", 10817])
+    _, stderr = capture_io do
+      plugin.requires_redmine(:version_or_higher => '2.2')
+    end
+    assert_match /requires Redmine/, stderr
   end
 
   def test_requires_redmine_plugin