diff --git a/.github/docs/openapi3.txt b/.github/docs/openapi3.txt
index 3ce7ed959..82a5e0bc8 100644
--- a/.github/docs/openapi3.txt
+++ b/.github/docs/openapi3.txt
@@ -1,6 +1,6 @@
 const ParameterInPath = "path" ...
 const TypeArray = "array" ...
-const FormatOfStringForUUIDOfRFC4122 = `^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}$` ...
+const FormatOfStringForUUIDOfRFC4122 = `^(?:[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000)$` ...
 const SerializationSimple = "simple" ...
 var SchemaErrorDetailsDisabled = false ...
 var CircularReferenceCounter = 3
diff --git a/openapi3/schema_formats.go b/openapi3/schema_formats.go
index ecbc0ebfa..ea38400c2 100644
--- a/openapi3/schema_formats.go
+++ b/openapi3/schema_formats.go
@@ -9,7 +9,7 @@ import (
 
 const (
 	// FormatOfStringForUUIDOfRFC4122 is an optional predefined format for UUID v1-v5 as specified by RFC4122
-	FormatOfStringForUUIDOfRFC4122 = `^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}$`
+	FormatOfStringForUUIDOfRFC4122 = `^(?:[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000)$`
 
 	// FormatOfStringForEmail pattern catches only some suspiciously wrong-looking email addresses.
 	// Use DefineStringFormat(...) if you need something stricter.