diff --git a/doc/html/changelog.html b/doc/html/changelog.html
index 1344ee06..3e14ccbc 100644
--- a/doc/html/changelog.html
+++ b/doc/html/changelog.html
@@ -115,12 +115,12 @@
 				</ul>
 			</li>
 			<li>
-				Interface changes (see also the <a href="http://flac.sourceforge.net/api/group__porting__1__2__1__to__1__2__2.html">porting guide</a> for specific instructions on porting to FLAC 1.2.2):
+				Interface changes:
 				<ul>
 					<li>
 						libFLAC:
 						<ul>
-							<li>(none)</li>
+							<li><b>Added</b> FLAC__format_blocksize_is_subset()</li>
 						</ul>
 					</li>
 					<li>
@@ -213,7 +213,7 @@
 				</ul>
 			</li>
 			<li>
-				Interface changes (see also the <a href="http://flac.sourceforge.net/api/group__porting__1__2__0__to__1__2__1.html">porting guide</a> for specific instructions on porting to FLAC 1.2.1):
+				Interface changes:
 				<ul>
 					<li>
 						libFLAC:
diff --git a/include/FLAC/format.h b/include/FLAC/format.h
index 83ec9653..ad118244 100644
--- a/include/FLAC/format.h
+++ b/include/FLAC/format.h
@@ -879,6 +879,18 @@ extern FLAC_API const unsigned FLAC__STREAM_METADATA_LENGTH_LEN; /**< == 24 (bit
  */
 FLAC_API FLAC__bool FLAC__format_sample_rate_is_valid(unsigned sample_rate);
 
+/** Tests that a blocksize at the given sample rate is valid for the FLAC
+ *  subset.
+ *
+ * \param blocksize    The blocksize to test for compliance.
+ * \param sample_rate  The sample rate is needed, since the valid subset
+ *                     blocksize depends on the sample rate.
+ * \retval FLAC__bool
+ *    \c true if the given blocksize conforms to the specification for the
+ *    subset at the given sample rate, else \c false.
+ */
+FLAC_API FLAC__bool FLAC__format_blocksize_is_subset(unsigned blocksize, unsigned sample_rate);
+
 /** Tests that a sample rate is valid for the FLAC subset.  The subset rules
  *  for valid sample rates are slightly more complex since the rate has to
  *  be expressible completely in the frame header.
diff --git a/src/libFLAC/format.c b/src/libFLAC/format.c
index be47146f..b795ac5c 100644
--- a/src/libFLAC/format.c
+++ b/src/libFLAC/format.c
@@ -223,6 +223,16 @@ FLAC_API FLAC__bool FLAC__format_sample_rate_is_valid(unsigned sample_rate)
 		return true;
 }
 
+FLAC_API FLAC__bool FLAC__format_blocksize_is_subset(unsigned blocksize, unsigned sample_rate)
+{
+	if(blocksize > 16384)
+		return false;
+	else if(sample_rate <= 48000 && blocksize > 4608)
+		return false;
+	else
+		return true;
+}
+
 FLAC_API FLAC__bool FLAC__format_sample_rate_is_subset(unsigned sample_rate)
 {
 	if(