diff --git a/library/pk.c b/library/pk.c
index d080c75..d8801b5 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -94,6 +94,7 @@
             return( &mbedtls_ecdsa_info );
 #endif
         /* MBEDTLS_PK_RSA_ALT omitted on purpose */
+        /* MBEDTLS_PK_OPAQUE omitted on purpose: they can't be built by parsing */
         default:
             return( NULL );
     }
@@ -107,8 +108,11 @@
     if( ctx == NULL || info == NULL || ctx->pk_info != NULL )
         return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
 
-    if( ( ctx->pk_ctx = info->ctx_alloc_func() ) == NULL )
-        return( MBEDTLS_ERR_PK_ALLOC_FAILED );
+    if( info->ctx_alloc_func != NULL )
+    {
+        if( ( ctx->pk_ctx = info->ctx_alloc_func( ) ) == NULL )
+            return( MBEDTLS_ERR_PK_ALLOC_FAILED );
+    }
 
     ctx->pk_info = info;
 
@@ -312,24 +316,31 @@
 int mbedtls_pk_check_pair( const mbedtls_pk_context *pub, const mbedtls_pk_context *prv )
 {
     if( pub == NULL || pub->pk_info == NULL ||
-        prv == NULL || prv->pk_info == NULL ||
-        prv->pk_info->check_pair_func == NULL )
+        prv == NULL || prv->pk_info == NULL )
     {
         return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
     }
 
+    if( pub->pk_info == prv->pk_info && pub->pk_ctx == prv->pk_ctx )
+        return( 0 );
+
+    if( prv->pk_info->check_pair_func == NULL )
+    {
+        return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
+    }
+
     if( prv->pk_info->type == MBEDTLS_PK_RSA_ALT )
     {
         if( pub->pk_info->type != MBEDTLS_PK_RSA )
             return( MBEDTLS_ERR_PK_TYPE_MISMATCH );
     }
-    else
+    else if( prv->pk_info->type != MBEDTLS_PK_OPAQUE )
     {
         if( pub->pk_info != prv->pk_info )
             return( MBEDTLS_ERR_PK_TYPE_MISMATCH );
     }
 
-    return( prv->pk_info->check_pair_func( pub->pk_ctx, prv->pk_ctx ) );
+    return( prv->pk_info->check_pair_func( pub, prv->pk_ctx ) );
 }
 
 /*
@@ -384,7 +395,9 @@
 }
 
 /*
- * Access the PK type
+ * Access the PK type.
+ * For an opaque key pair object, this does not give any information on the
+ * underlying cryptographic material.
  */
 mbedtls_pk_type_t mbedtls_pk_get_type( const mbedtls_pk_context *ctx )
 {