diff --git a/ChangeLog b/ChangeLog
index a3171d7..92f1bae 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.x.x branch released xxxx-xx-xx
+
+Security
+   * Set PEM buffer to zero before freeing it, to avoid decoded private keys
+     being leaked to memory after release.
+
 = mbed TLS 1.3.21 branch released 2017-08-10
 
 Security
diff --git a/library/pem.c b/library/pem.c
index b2c16c2..76905b3 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -389,6 +389,8 @@
 
 void pem_free( pem_context *ctx )
 {
+    if ( ctx->buf != NULL )
+        polarssl_zeroize( ctx->buf, ctx->buflen );
     polarssl_free( ctx->buf );
     polarssl_free( ctx->info );