diff --git a/k9mail/src/main/java/com/fsck/k9/message/html/HtmlConverter.java b/k9mail/src/main/java/com/fsck/k9/message/html/HtmlConverter.java
index 35d82ae53..e037c3f1d 100644
--- a/k9mail/src/main/java/com/fsck/k9/message/html/HtmlConverter.java
+++ b/k9mail/src/main/java/com/fsck/k9/message/html/HtmlConverter.java
@@ -237,6 +237,11 @@ public class HtmlConverter {
             "style=\"margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid $$COLOR$$; padding-left: 1ex;\">";
     private static final String HTML_BLOCKQUOTE_END = "</blockquote>";
     private static final String HTML_NEWLINE = "<br />";
+    private static final Pattern ASCII_PATTERN_FOR_HR = Pattern.compile(
+            "(^|\\Q" + HTML_NEWLINE + "\\E)\\s*((\\Q" + HTML_NEWLINE + "\\E)*" +
+            "((((\\Q" + HTML_NEWLINE + "\\E){0,2}([-=_]{3,})(\\Q" + HTML_NEWLINE +
+            "\\E){0,2})|(([-=_]{2,} ?)(8&lt;|<gt>8|%&lt;|<gt>%)" +
+            "( ?[-=_]{2,})))+(\\Q" + HTML_NEWLINE + "\\E|$)))");
 
     /**
      * Convert a text string into an HTML document.
@@ -329,8 +334,7 @@ public class HtmlConverter {
                    HTML_BLOCKQUOTE_END + "$1"
                );
 
-        // Replace lines of -,= or _ with horizontal rules
-        text = text.replaceAll("\\s*([-=_]{30,}+)\\s*", "<hr />");
+        text = ASCII_PATTERN_FOR_HR.matcher(text).replaceAll("<hr>");
 
         StringBuffer sb = new StringBuffer(text.length() + TEXT_TO_HTML_EXTRA_BUFFER_LENGTH);
 
diff --git a/k9mail/src/test/java/com/fsck/k9/message/html/HtmlConverterTest.java b/k9mail/src/test/java/com/fsck/k9/message/html/HtmlConverterTest.java
index 57e6105e6..28ce3cf3f 100644
--- a/k9mail/src/test/java/com/fsck/k9/message/html/HtmlConverterTest.java
+++ b/k9mail/src/test/java/com/fsck/k9/message/html/HtmlConverterTest.java
@@ -207,4 +207,105 @@ public class HtmlConverterTest {
                 "http://example.com/" +
                 "</a>", outputBuffer.toString());
     }
+
+    @Test
+    public void issue2259Spec() {
+        String text = "text\n" +
+                "---------------------------\n" +
+                "some other text\n" +
+                "===========================\n" +
+                "more text\n" +
+                "-=-=-=-=-=-=-=-=-=-=-=-=-=-\n" +
+                "scissors below\n" +
+                "-- >8 --\n" +
+                "other direction\n" +
+                "-- 8< --\n" +
+                "end";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">text<hr>" +
+                "some other text<hr>" +
+                "more text<hr>" +
+                "scissors below<hr>" +
+                "other direction<hr>" +
+                "end</pre>",
+                result);
+    }
+
+    @Test
+    public void dashesContainingSpacesIgnoredAsHR() {
+        String text = "hello\n--- --- --- --- ---\nfoo bar";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">hello<br />--- --- --- --- ---<br />foo bar</pre>",
+                result);
+    }
+
+    @Test
+    public void mergeConsecutiveBreaksIntoOne() {
+        String text = "hello\n------------\n---------------\nfoo bar";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">hello<hr>foo bar</pre>", result);
+    }
+
+    @Test
+    public void dashedHorizontalRulePrefixedWithTextIgnoredAsHR() {
+        String text = "hello----\n\n";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">hello----<br /><br /></pre>", result);
+    }
+
+    @Test
+    public void doubleMinusIgnoredAsHR() {
+        String text = "--\n";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">--<br /></pre>", result);
+    }
+
+    @Test
+    public void doubleEqualsIgnoredAsHR() {
+        String text = "==\n";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">==<br /></pre>", result);
+    }
+
+    @Test
+    public void doubleUnderscoreIgnoredAsHR() {
+        String text = "__\n";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">__<br /></pre>", result);
+    }
+
+    @Test
+    public void anyTripletIsHRuledOut() {
+        String text = "--=\n-=-\n===\n___\n\n";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\"><hr></pre>", result);
+    }
+
+    @Test
+    public void replaceSpaceSeparatedDashesWithHR() {
+        String text = "hello\n---------------------------\nfoo bar";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">hello<hr>foo bar</pre>", result);
+    }
+
+    @Test
+    public void replacementWithHRAtBeginning() {
+        String text = "---------------------------\nfoo bar";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\"><hr>foo bar</pre>", result);
+    }
+
+    @Test
+    public void replacementWithHRAtEnd() {
+        String text = "hello\n__________________________________";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">hello<hr></pre>", result);
+    }
+
+    @Test
+    public void replacementOfScissorsByHR() {
+        String text = "hello\n-- %< -------------- >8 --\nworld\n";
+        String result = HtmlConverter.textToHtml(text);
+        assertEquals("<pre class=\"k9mail\">hello<hr>world<br /></pre>", result);
+    }
 }