diff --git a/internal/converter/testdata/oneof.go b/internal/converter/testdata/oneof.go
index a1824c40..95f63a49 100644
--- a/internal/converter/testdata/oneof.go
+++ b/internal/converter/testdata/oneof.go
@@ -5,6 +5,9 @@ const OneOf = `{
     "$ref": "#/definitions/OneOf",
     "definitions": {
         "OneOf": {
+            "required": [
+                "something"
+            ],
             "properties": {
                 "bar": {
                     "$ref": "#/definitions/samples.OneOf.Bar",
@@ -20,15 +23,35 @@ const OneOf = `{
             },
             "additionalProperties": true,
             "type": "object",
-            "oneOf": [
-                {
-                    "required": [
-                        "bar"
-                    ]
-                },
+            "allOf": [
                 {
-                    "required": [
-                        "baz"
+                    "oneOf": [
+                        {
+                            "not": {
+                                "anyOf": [
+                                    {
+                                        "required": [
+                                            "bar"
+                                        ]
+                                    },
+                                    {
+                                        "required": [
+                                            "baz"
+                                        ]
+                                    }
+                                ]
+                            }
+                        },
+                        {
+                            "required": [
+                                "bar"
+                            ]
+                        },
+                        {
+                            "required": [
+                                "baz"
+                            ]
+                        }
                     ]
                 }
             ],
diff --git a/internal/converter/types.go b/internal/converter/types.go
index 50490dc9..0b137087 100644
--- a/internal/converter/types.go
+++ b/internal/converter/types.go
@@ -625,13 +625,21 @@ func (c *Converter) recursiveConvertMessageType(curPkg *ProtoPackage, msgDesc *d
 		c.logger.WithField("field_name", fieldDesc.GetName()).WithField("type", recursedJSONSchemaType.Type).Trace("Converted field")
 
 		// If this field is part of a OneOf declaration then build that here:
-		if c.Flags.EnforceOneOf && fieldDesc.OneofIndex != nil {
+		if c.Flags.EnforceOneOf && fieldDesc.OneofIndex != nil && !fieldDesc.GetProto3Optional() {
+			for {
+				if *fieldDesc.OneofIndex < int32(len(jsonSchemaType.AllOf)) {
+					break
+				}
+				var notAnyOf = &jsonschema.Type{Not: &jsonschema.Type{AnyOf: []*jsonschema.Type{}}}
+				jsonSchemaType.AllOf = append(jsonSchemaType.AllOf, &jsonschema.Type{OneOf: []*jsonschema.Type{notAnyOf}})
+			}
 			if c.Flags.UseJSONFieldnamesOnly {
-				jsonSchemaType.OneOf = append(jsonSchemaType.OneOf, &jsonschema.Type{Required: []string{fieldDesc.GetJsonName()}})
+				jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf = append(jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf, &jsonschema.Type{Required: []string{fieldDesc.GetJsonName()}})
+				jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf[0].Not.AnyOf = append(jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf[0].Not.AnyOf, &jsonschema.Type{Required: []string{fieldDesc.GetJsonName()}})
 			} else {
-				jsonSchemaType.OneOf = append(jsonSchemaType.OneOf, &jsonschema.Type{Required: []string{fieldDesc.GetName()}})
+				jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf = append(jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf, &jsonschema.Type{Required: []string{fieldDesc.GetName()}})
+				jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf[0].Not.AnyOf = append(jsonSchemaType.AllOf[*fieldDesc.OneofIndex].OneOf[0].Not.AnyOf, &jsonschema.Type{Required: []string{fieldDesc.GetName()}})
 			}
-
 		}
 
 		// Figure out which field names we want to use:
@@ -646,9 +654,13 @@ func (c *Converter) recursiveConvertMessageType(curPkg *ProtoPackage, msgDesc *d
 		}
 
 		// Enforce all_fields_required:
-		if messageFlags.AllFieldsRequired && len(jsonSchemaType.OneOf) == 0 && jsonSchemaType.Properties != nil {
-			for _, property := range jsonSchemaType.Properties.Keys() {
-				jsonSchemaType.Required = append(jsonSchemaType.Required, property)
+		if messageFlags.AllFieldsRequired {
+			if fieldDesc.OneofIndex == nil && !fieldDesc.GetProto3Optional() {
+				if c.Flags.UseJSONFieldnamesOnly {
+					jsonSchemaType.Required = append(jsonSchemaType.Required, fieldDesc.GetJsonName())
+				} else {
+					jsonSchemaType.Required = append(jsonSchemaType.Required, fieldDesc.GetName())
+				}
 			}
 		}
 
diff --git a/jsonschemas/OneOf.json b/jsonschemas/OneOf.json
index 298bdd1a..bc6f3c38 100644
--- a/jsonschemas/OneOf.json
+++ b/jsonschemas/OneOf.json
@@ -18,15 +18,35 @@
             },
             "additionalProperties": true,
             "type": "object",
-            "oneOf": [
+            "allOf": [
                 {
-                    "required": [
-                        "bar"
-                    ]
-                },
-                {
-                    "required": [
-                        "baz"
+                    "oneOf": [
+                        {
+                            "not": {
+                                "anyOf": [
+                                    {
+                                        "required": [
+                                            "bar"
+                                        ]
+                                    },
+                                    {
+                                        "required": [
+                                            "baz"
+                                        ]
+                                    }
+                                ]
+                            }
+                        },
+                        {
+                            "required": [
+                                "bar"
+                            ]
+                        },
+                        {
+                            "required": [
+                                "baz"
+                            ]
+                        }
                     ]
                 }
             ],