diff --git a/lib/redmine/thumbnail.rb b/lib/redmine/thumbnail.rb
index 2fa33a13f..c2a2a2eaa 100644
--- a/lib/redmine/thumbnail.rb
+++ b/lib/redmine/thumbnail.rb
@@ -21,16 +21,18 @@ module Redmine
   module Thumbnail
     extend Redmine::Utils::Shell
 
+    CONVERT_BIN = (Redmine::Configuration['imagemagick_convert_command'] || 'convert').freeze
+
     # Generates a thumbnail for the source image to target
     def self.generate(source, target, size)
+      return nil unless convert_available?
       unless File.exists?(target)
         directory = File.dirname(target)
         unless File.exists?(directory)
           FileUtils.mkdir_p directory
         end
-        bin = Redmine::Configuration['imagemagick_convert_command'] || 'convert'
         size_option = "#{size}x#{size}>"
-        cmd = "#{shell_quote bin} #{shell_quote source} -thumbnail #{shell_quote size_option} #{shell_quote target}"
+        cmd = "#{shell_quote CONVERT_BIN} #{shell_quote source} -thumbnail #{shell_quote size_option} #{shell_quote target}"
         unless system(cmd)
           logger.error("Creating thumbnail failed (#{$?}):\nCommand: #{cmd}")
           return nil
@@ -39,6 +41,14 @@ module Redmine
       target
     end
 
+    def self.convert_available?
+      return @convert_available if defined?(@convert_available)
+      logger.warn("testing for convert...")
+      @convert_available = system("#{shell_quote CONVERT_BIN} -version") rescue false
+      logger.warn("Imagemagick's convert binary (#{CONVERT_BIN}) not available") unless @convert_available
+      @convert_available
+    end
+
     def self.logger
       Rails.logger
     end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 6f5ab98a4..c4c956953 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -129,10 +129,7 @@ class ActiveSupport::TestCase
   end
 
   def self.convert_installed?
-    bin = Redmine::Configuration['imagemagick_convert_command'] || 'convert'
-    system("#{bin} -version")
-  rescue
-    false
+    Redmine::Thumbnail.convert_available?
   end
 
   # Returns the path to the test +vendor+ repository