diff --git a/library/pem.c b/library/pem.c
index a09257c..ea36df8 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -331,6 +331,7 @@
 
     if( ( ret = mbedtls_base64_decode( buf, len, &len, s1, s2 - s1 ) ) != 0 )
     {
+        mbedtls_zeroize( buf, len );
         mbedtls_free( buf );
         return( MBEDTLS_ERR_PEM_INVALID_DATA + ret );
     }