diff --git a/modules/openapi-generator/src/main/resources/typescript-angular/modelTaggedUnion.mustache b/modules/openapi-generator/src/main/resources/typescript-angular/modelTaggedUnion.mustache
index 8e4507f2c022..38c3a582319f 100644
--- a/modules/openapi-generator/src/main/resources/typescript-angular/modelTaggedUnion.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-angular/modelTaggedUnion.mustache
@@ -17,7 +17,14 @@ export interface {{classname}} { {{>modelGenericAdditionalProperties}}
 
 {{/parent}}
 {{^parent}}
+{{#oneOf}}
+{{#-first}}
+{{>modelOneOf}}
+{{/-first}}
+{{/oneOf}}
+{{^oneOf}}
 {{>modelGeneric}}
+{{/oneOf}}
 
 {{/parent}}
 {{/discriminator}}
\ No newline at end of file
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java
index dbece37188b2..4e9b3798a728 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/typescriptangular/TypeScriptAngularClientCodegenTest.java
@@ -330,6 +330,25 @@ public void testTaggedUnionImports() throws Exception {
         );
     }
 
+    @Test
+    public void testTaggedUnionsOneOfWithoutDiscriminator() throws Exception {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("typescript-angular")
+                .setInputSpec("src/test/resources/3_0/typescript-angular/issue_20859.yaml")
+                .addAdditionalProperty(TypeScriptAngularClientCodegen.TAGGED_UNIONS, true)
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        new DefaultGenerator().opts(configurator.toClientOptInput()).generate();
+
+        TestUtils.assertFileContains(
+                Paths.get(output + "/model/zooInner.ts"),
+                "export type ZooInner = Cat | Dog;"
+        );
+    }
+
     @Test
     public void testModelNameMappings() throws Exception {
         final String specPath = "src/test/resources/2_0/issue_8289.json";
diff --git a/modules/openapi-generator/src/test/resources/3_0/typescript-angular/issue_20859.yaml b/modules/openapi-generator/src/test/resources/3_0/typescript-angular/issue_20859.yaml
new file mode 100644
index 000000000000..cf3356f39ab9
--- /dev/null
+++ b/modules/openapi-generator/src/test/resources/3_0/typescript-angular/issue_20859.yaml
@@ -0,0 +1,47 @@
+openapi: 3.0.0
+info:
+  title: OpenAPI definition
+  version: v0
+paths:
+  /api/test/zoo:
+    get:
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Zoo'
+components:
+  schemas:
+    Animal:
+      type: object
+      discriminator:
+        propertyName: type
+      properties:
+        type:
+          type: string
+      required:
+        - type
+    Cat:
+      allOf:
+        - $ref: '#/components/schemas/Animal'
+        - type: object
+          properties:
+            purrFrequency:
+              type: integer
+              format: int32
+    Dog:
+      allOf:
+        - $ref: '#/components/schemas/Animal'
+        - type: object
+          properties:
+            barkVolume:
+              type: integer
+              format: int32
+    Zoo:
+      type: array
+      items:
+        oneOf:
+          - $ref: '#/components/schemas/Cat'
+          - $ref: '#/components/schemas/Dog'