diff --git a/src/com/fsck/k9/mail/filter/EOLConvertingOutputStream.java b/src/com/fsck/k9/mail/filter/EOLConvertingOutputStream.java
index ea89c3083..c19780a36 100644
--- a/src/com/fsck/k9/mail/filter/EOLConvertingOutputStream.java
+++ b/src/com/fsck/k9/mail/filter/EOLConvertingOutputStream.java
@@ -5,8 +5,11 @@ import java.io.IOException;
 import java.io.OutputStream;
 
 public class EOLConvertingOutputStream extends FilterOutputStream {
+    private static final int CR = '\r';
+    private static final int LF = '\n';
     private int lastChar;
-    private boolean ignoreNextIfLF = false;
+    private static final int IGNORE_LF = Integer.MIN_VALUE;
+
 
     public EOLConvertingOutputStream(OutputStream out) {
         super(out);
@@ -14,26 +17,27 @@ public class EOLConvertingOutputStream extends FilterOutputStream {
 
     @Override
     public void write(int oneByte) throws IOException {
-        if (!ignoreNextIfLF) {
-            if ((oneByte == '\n') && (lastChar != '\r')) {
-                super.write('\r');
-            }
-            super.write(oneByte);
-            lastChar = oneByte;
+        if (oneByte == LF && lastChar == IGNORE_LF) {
+            lastChar = LF;
+            return;
         }
-        ignoreNextIfLF = false;
+        if (oneByte == LF && lastChar != CR) {
+            super.write(CR);
+        } else if (oneByte != LF && lastChar == CR) {
+            super.write(LF);
+        }
+        super.write(oneByte);
+        lastChar = oneByte;
     }
 
     @Override
     public void flush() throws IOException {
-        if (lastChar == '\r') {
-            super.write('\n');
-            lastChar = '\n';
-
+        if (lastChar == CR) {
+            super.write(LF);
             // We have to ignore the next character if it is <LF>. Otherwise it
             // will be expanded to an additional <CR><LF> sequence although it
             // belongs to the one just completed.
-            ignoreNextIfLF = true;
+            lastChar = IGNORE_LF;
         }
         super.flush();
     }
diff --git a/tests-on-jvm/src/com/fsck/k9/mail/filter/EOLConvertingOutputStreamTest.java b/tests-on-jvm/src/com/fsck/k9/mail/filter/EOLConvertingOutputStreamTest.java
new file mode 100644
index 000000000..ebb9dac64
--- /dev/null
+++ b/tests-on-jvm/src/com/fsck/k9/mail/filter/EOLConvertingOutputStreamTest.java
@@ -0,0 +1,69 @@
+package com.fsck.k9.mail.filter;
+
+import junit.framework.TestCase;
+
+import java.io.ByteArrayOutputStream;
+
+public class EOLConvertingOutputStreamTest extends TestCase {
+    private EOLConvertingOutputStream subject;
+    private ByteArrayOutputStream out;
+
+    @Override
+    public void setUp() throws Exception {
+        super.setUp();
+        out = new ByteArrayOutputStream();
+        subject = new EOLConvertingOutputStream(out);
+    }
+
+    public void testFilterWithoutCRorLF() throws Exception {
+        subject.write("Unchanged".getBytes());
+        subject.flush();
+        assertEquals("Unchanged", out.toString());
+    }
+
+    public void testFilterWithCRLF() throws Exception {
+        subject.write("Filter\r\nNext Line".getBytes());
+        subject.flush();
+        assertEquals("Filter\r\nNext Line", out.toString());
+    }
+
+    public void testFilterWithJustCR() throws Exception {
+        subject.write("\n\n\n".getBytes());
+        subject.flush();
+        assertEquals("\r\n\r\n\r\n", out.toString());
+    }
+
+    public void testFilterWithCR() throws Exception {
+        subject.write("Filter\rNext Line".getBytes());
+        subject.flush();
+        assertEquals("Filter\r\nNext Line", out.toString());
+    }
+
+    public void testFilterWithLF() throws Exception {
+        subject.write("Filter\nNext Line".getBytes());
+        subject.flush();
+        assertEquals("Filter\r\nNext Line", out.toString());
+    }
+
+    public void testFlushWithCR() throws Exception {
+        subject.write("Flush\r".getBytes());
+        subject.flush();
+        assertEquals("Flush\r\n", out.toString());
+        subject.write("\n\n\n".getBytes());
+        assertEquals("Flush\r\n\r\n\r\n", out.toString());
+    }
+
+    public void testFlushWithCRNotFollowedByLF() throws Exception {
+        subject.write("Flush\r".getBytes());
+        subject.flush();
+        subject.write("Next line".getBytes());
+        assertEquals("Flush\r\nNext line", out.toString());
+    }
+
+    public void testFlushWithLF() throws Exception {
+        subject.write("Flush\n".getBytes());
+        subject.flush();
+        subject.write("\n".getBytes());
+        assertEquals("Flush\r\n\r\n", out.toString());
+    }
+}