diff --git a/lib/redmine/export/pdf.rb b/lib/redmine/export/pdf.rb
index 2ca6deb5c..448f7273f 100644
--- a/lib/redmine/export/pdf.rb
+++ b/lib/redmine/export/pdf.rb
@@ -455,8 +455,12 @@ module Redmine
           txt ||= ''
           if txt.respond_to?(:force_encoding)
             txt.force_encoding('UTF-8')
-            txt = txt.encode(l(:general_pdf_encoding), :invalid => :replace,
-                              :undef => :replace, :replace => '?')
+            if l(:general_pdf_encoding).upcase != 'UTF-8'
+              txt = txt.encode(l(:general_pdf_encoding), :invalid => :replace,
+                               :undef => :replace, :replace => '?')
+            else
+              txt = Redmine::CodesetUtil.replace_invalid_utf8(txt)
+            end
             txt.force_encoding('ASCII-8BIT')
           else
             ic ||= Iconv.new(l(:general_pdf_encoding), 'UTF-8')
diff --git a/test/unit/lib/redmine/export/pdf_test.rb b/test/unit/lib/redmine/export/pdf_test.rb
index 6cd438ddf..5c74f1aa2 100644
--- a/test/unit/lib/redmine/export/pdf_test.rb
+++ b/test/unit/lib/redmine/export/pdf_test.rb
@@ -58,4 +58,44 @@ class PdfTest < ActiveSupport::TestCase
                    Redmine::Export::PDF::RDMPdfEncoding::rdm_pdf_iconv(ic, utf8_txt_3)
     end
   end
+
+  def test_rdm_pdf_iconv_invalid_utf8_should_be_replaced_en
+    set_language_if_valid 'en'
+    assert_equal 'UTF-8', l(:general_pdf_encoding)
+    str1 = "Texte encod\xe9 en ISO-8859-1"
+    str2 = "\xe9a\xe9b\xe9c\xe9d\xe9e test"
+    str1.force_encoding("UTF-8") if str1.respond_to?(:force_encoding)
+    str2.force_encoding("ASCII-8BIT") if str2.respond_to?(:force_encoding)
+    if RUBY_VERSION < '1.9'
+      ic = Iconv.new(l(:general_pdf_encoding), 'UTF-8')
+    end
+    txt_1 = Redmine::Export::PDF::RDMPdfEncoding::rdm_pdf_iconv(ic, str1)
+    txt_2 = Redmine::Export::PDF::RDMPdfEncoding::rdm_pdf_iconv(ic, str2)
+    if txt_1.respond_to?(:force_encoding)
+      assert_equal "ASCII-8BIT", txt_1.encoding.to_s
+      assert_equal "ASCII-8BIT", txt_2.encoding.to_s
+    end
+    assert_equal "Texte encod? en ISO-8859-1", txt_1
+    assert_equal "?a?b?c?d?e test", txt_2
+  end
+
+  def test_rdm_pdf_iconv_invalid_utf8_should_be_replaced_ja
+    set_language_if_valid 'ja'
+    assert_equal 'CP932', l(:general_pdf_encoding)
+    str1 = "Texte encod\xe9 en ISO-8859-1"
+    str2 = "\xe9a\xe9b\xe9c\xe9d\xe9e test"
+    str1.force_encoding("UTF-8") if str1.respond_to?(:force_encoding)
+    str2.force_encoding("ASCII-8BIT") if str2.respond_to?(:force_encoding)
+    if RUBY_VERSION < '1.9'
+      ic = Iconv.new(l(:general_pdf_encoding), 'UTF-8')
+    end
+    txt_1 = Redmine::Export::PDF::RDMPdfEncoding::rdm_pdf_iconv(ic, str1)
+    txt_2 = Redmine::Export::PDF::RDMPdfEncoding::rdm_pdf_iconv(ic, str2)
+    if txt_1.respond_to?(:force_encoding)
+      assert_equal "ASCII-8BIT", txt_1.encoding.to_s
+      assert_equal "ASCII-8BIT", txt_2.encoding.to_s
+    end
+    assert_equal "Texte encod? en ISO-8859-1", txt_1
+    assert_equal "?a?b?c?d?e test", txt_2
+  end
 end