diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index 72f5a10..56f23c9 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -46,6 +46,10 @@
 
 void mbedtls_x509write_crt_free(mbedtls_x509write_cert *ctx)
 {
+    if (ctx == NULL) {
+        return;
+    }
+
     mbedtls_asn1_free_named_data_list(&ctx->subject);
     mbedtls_asn1_free_named_data_list(&ctx->issuer);
     mbedtls_asn1_free_named_data_list(&ctx->extensions);