diff --git a/library/rsa.c b/library/rsa.c
index c3b54af..36424bd 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -1764,6 +1764,9 @@
                       hash != NULL );
     RSA_VALIDATE_RET( sig != NULL );
 
+    if( ctx->padding != MBEDTLS_RSA_PKCS_V21 )
+        return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
+
     if( f_rng == NULL )
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
 
@@ -2054,6 +2057,9 @@
                       hash != NULL );
     RSA_VALIDATE_RET( sig != NULL );
 
+    if( ctx->padding != MBEDTLS_RSA_PKCS_V15 )
+        return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
+
     /*
      * Prepare PKCS1-v1.5 encoding (padding and hash identifier)
      */