diff --git a/ChangeLog b/ChangeLog
index aa96b1848..998baed0e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 2.2.R0released 2015-10-xx
+
+Security
+   * Fix potential buffer overflow in some asn1_write_xxx() functions.
+     Cannot be triggered remotely unless you create X.509 certificates based
+     on untrusted input or write keys of untrusted origin. Found by Guido
+     Vranken, Interlworks.
+
 = mbed TLS 2.1.2 released 2015-10-06
 
 Security
diff --git a/library/asn1write.c b/library/asn1write.c
index dd5a7455e..fd262a50b 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -87,7 +87,7 @@ int mbedtls_asn1_write_raw_buffer( unsigned char **p, unsigned char *start,
 {
     size_t len = 0;
 
-    if( *p - start < (int) size )
+    if( *p < start || (size_t)( *p - start ) < size )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
 
     len = size;
@@ -107,7 +107,7 @@ int mbedtls_asn1_write_mpi( unsigned char **p, unsigned char *start, const mbedt
     //
     len = mbedtls_mpi_size( X );
 
-    if( *p - start < (int) len )
+    if( *p < start || (size_t)( *p - start ) < len )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
 
     (*p) -= len;
@@ -270,7 +270,7 @@ int mbedtls_asn1_write_bitstring( unsigned char **p, unsigned char *start,
 
     // Calculate byte length
     //
-    if( *p - start < (int) size + 1 )
+    if( *p < start || (size_t)( *p - start ) < size + 1 )
         return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
 
     len = size + 1;