diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 3fd6e34..8c60428 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -916,6 +916,9 @@
     }
 
     /* opaque psk<0..2^16-1>; */
+    if( end - p < 2 + (int) ssl->psk_len )
+            return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
+
     *(p++) = (unsigned char)( ssl->psk_len >> 8 );
     *(p++) = (unsigned char)( ssl->psk_len      );
     memcpy( p, ssl->psk, ssl->psk_len );
@@ -3784,6 +3787,14 @@
     if( psk == NULL || psk_identity == NULL )
         return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
 
+    /*
+     * The length will be check later anyway, but in case it is obviously
+     * too large, better abort now. The PMS is as follows:
+     * other_len (2 bytes) + other + psk_len (2 bytes) + psk
+     */
+    if( psk_len + 4 > POLARSSL_PREMASTER_SIZE )
+        return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
+
     if( ssl->psk != NULL )
     {
         polarssl_free( ssl->psk );