diff --git a/ChangeLog b/ChangeLog
index 0f9d6bd..86c6ef5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -204,6 +204,8 @@
 Bugfix
    * Fix an issue with MicroBlaze support in bn_mul.h which was causing the
      build to fail. Found by zv-io. Fixes #1651.
+   * Fix undefined shifts with negative values in certificates parsing
+     (found by Catena cyber using oss-fuzz)
 
 Changes
    * Support TLS testing in out-of-source builds using cmake. Fixes #1193.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 73e4391..82d76af 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -3332,8 +3332,8 @@
 
     msg = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
 
-    lifetime = ( msg[0] << 24 ) | ( msg[1] << 16 ) |
-               ( msg[2] <<  8 ) | ( msg[3]       );
+    lifetime = ( ((uint32_t) msg[0]) << 24 ) | ( msg[1] << 16 ) |
+               ( msg[2] << 8 ) | ( msg[3] );
 
     ticket_len = ( msg[4] << 8 ) | ( msg[5] );
 
diff --git a/library/x509_crt.c b/library/x509_crt.c
index 290c1eb..89194b3 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -163,6 +163,9 @@
 static int x509_profile_check_md_alg( const mbedtls_x509_crt_profile *profile,
                                       mbedtls_md_type_t md_alg )
 {
+    if( md_alg == MBEDTLS_MD_NONE )
+        return( -1 );
+
     if( ( profile->allowed_mds & MBEDTLS_X509_ID_FLAG( md_alg ) ) != 0 )
         return( 0 );
 
@@ -176,6 +179,9 @@
 static int x509_profile_check_pk_alg( const mbedtls_x509_crt_profile *profile,
                                       mbedtls_pk_type_t pk_alg )
 {
+    if( pk_alg == MBEDTLS_PK_NONE )
+        return( -1 );
+
     if( ( profile->allowed_pks & MBEDTLS_X509_ID_FLAG( pk_alg ) ) != 0 )
         return( 0 );
 
@@ -208,6 +214,9 @@
     {
         const mbedtls_ecp_group_id gid = mbedtls_pk_ec( *pk )->grp.id;
 
+        if( gid == MBEDTLS_ECP_DP_NONE )
+            return( -1 );
+
         if( ( profile->allowed_curves & MBEDTLS_X509_ID_FLAG( gid ) ) != 0 )
             return( 0 );