diff --git a/programs/x509/cert_write.c b/programs/x509/cert_write.c
index 8bee0a666..d8660dc95 100644
--- a/programs/x509/cert_write.c
+++ b/programs/x509/cert_write.c
@@ -585,7 +585,7 @@ usage:
                     *subtype_value++ = '\0';
                 } else {
                     mbedtls_printf(
-                        "Invalid argument for option SAN: Entry should be separated by a colon\n");
+                        "Invalid argument for option SAN: Entry must be of the form TYPE:value\n");
                     goto usage;
                 }
                 if (strcmp(q, "RFC822") == 0) {