diff --git a/library/pem.c b/library/pem.c
index 8dd86a4..4c23373 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -387,6 +387,7 @@
 
 void mbedtls_pem_free( mbedtls_pem_context *ctx )
 {
+    memset( ctx->buf, 0, ctx->buflen );
     mbedtls_free( ctx->buf );
     mbedtls_free( ctx->info );