diff --git a/taglib/mpeg/mpegproperties.cpp b/taglib/mpeg/mpegproperties.cpp
index 8507f38d..b9ae8675 100644
--- a/taglib/mpeg/mpegproperties.cpp
+++ b/taglib/mpeg/mpegproperties.cpp
@@ -205,6 +205,11 @@ void MPEG::Properties::read(File *file)
 
     d->bitrate = firstHeader.bitrate();
 
+    // Look for the last MPEG audio frame to calculate the stream length.
+
+    // This actually finds the second last valid frame, since MPEG::Header requires
+    // the next frame header to check if the frame length is calculated correctly.
+
     long lastFrameOffset = file->lastFrameOffset();
     if(lastFrameOffset < 0) {
       debug("MPEG::Properties::read() -- Could not find an MPEG frame in the stream.");
diff --git a/tests/test_mpeg.cpp b/tests/test_mpeg.cpp
index 9b972382..455fde2c 100644
--- a/tests/test_mpeg.cpp
+++ b/tests/test_mpeg.cpp
@@ -93,10 +93,13 @@ public:
     CPPUNIT_ASSERT_EQUAL(44100, f.audioProperties()->sampleRate());
     CPPUNIT_ASSERT(!f.audioProperties()->xingHeader());
 
+    // This actually finds the second last valid frame, since MPEG::Header requires
+    // the next frame header to check if the frame length is calculated correctly.
+
     long last = f.lastFrameOffset();
     MPEG::Header lastHeader(&f, last);
 
-    while (!lastHeader.isValid()) {
+    while(!lastHeader.isValid()) {
       last = f.previousFrameOffset(last);
       lastHeader = MPEG::Header(&f, last);
     }