diff --git a/library/pem.c b/library/pem.c
index 534d071..969d492 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -478,8 +478,12 @@
     *p++ = '\0';
     *olen = p - buf;
 
+     /* Clean any remaining data previously written to the buffer */
+    memset( buf + *olen, 0, buf_len - *olen );
+
     mbedtls_free( encode_buf );
     return( 0 );
 }
 #endif /* MBEDTLS_PEM_WRITE_C */
 #endif /* MBEDTLS_PEM_PARSE_C || MBEDTLS_PEM_WRITE_C */
+