diff --git a/ChangeLog b/ChangeLog
index 51c5e2075..99df526ed 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,14 @@ Security
      CertificateVerify messages, to prevent SLOTH attacks against TLS 1.2.
      Introduced by interoperability fix for #513.
 
+Security
+   * Fixed a bug that caused freeing a buffer that was allocated on the stack,
+     when verifying the validity of a key on secp224k1. This could be
+     triggered remotely for example with a maliciously constructed certificate
+     and might have led to remote code execution on some exotic embedded
+     platforms. Reported independently by rongsaws and Regina Wilson.
+     CVE-2017-2784
+
 Bugfix
    * Fix output certificate verification flags set by x509_crt_verify_top() when
      traversing a chain of trusted CA. The issue would cause both flags,
diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index 9a6e8eb18..a2a5495a9 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -1213,7 +1213,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t
     int ret;
     size_t i;
     mbedtls_mpi M, R;
-    mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R];
+    mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R + 1];
 
     if( N->n < p_limbs )
         return( 0 );
@@ -1235,7 +1235,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t
     memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( mbedtls_mpi_uint ) );
     if( shift != 0 )
         MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &M, shift ) );
-    M.n += R.n - adjust; /* Make room for multiplication by R */
+    M.n += R.n; /* Make room for multiplication by R */
 
     /* N = A0 */
     if( mask != 0 )
@@ -1257,7 +1257,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t
     memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( mbedtls_mpi_uint ) );
     if( shift != 0 )
         MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &M, shift ) );
-    M.n += R.n - adjust; /* Make room for multiplication by R */
+    M.n += R.n; /* Make room for multiplication by R */
 
     /* N = A0 */
     if( mask != 0 )