diff --git a/api/src/main/resources/schema/workflow.yaml b/api/src/main/resources/schema/workflow.yaml
index 86e33868..bba84e95 100644
--- a/api/src/main/resources/schema/workflow.yaml
+++ b/api/src/main/resources/schema/workflow.yaml
@@ -202,6 +202,7 @@ $defs:
           call:
             type: string
             const: asyncapi
+            enum: [asyncapi]
           with:
             type: object
             title: AsyncApiArguments
@@ -247,6 +248,7 @@ $defs:
           call:
             type: string
             const: grpc
+            enum: [grpc]
           with:
             type: object
             title: GRPCArguments
@@ -301,7 +303,8 @@ $defs:
         properties:
           call:
             type: string
-            const: http
+            const: http 
+            enum: [http]
           with:
             type: object
             title: HTTPArguments
@@ -350,6 +353,7 @@ $defs:
           call:
             type: string
             const: openapi
+            enum: [openapi]
           with:
             type: object
             title: OpenAPIArguments
@@ -1351,4 +1355,4 @@ $defs:
     type: string
     title: RuntimeExpression
     description: A runtime expression.
-    pattern: "^\\s*\\$\\{.+\\}\\s*$"
\ No newline at end of file
+    pattern: "^\\s*\\$\\{.+\\}\\s*$"
diff --git a/api/src/test/java/io/serverlessworkflow/api/ApiTest.java b/api/src/test/java/io/serverlessworkflow/api/ApiTest.java
index ac5f7532..0a32173d 100644
--- a/api/src/test/java/io/serverlessworkflow/api/ApiTest.java
+++ b/api/src/test/java/io/serverlessworkflow/api/ApiTest.java
@@ -18,6 +18,7 @@
 import static io.serverlessworkflow.api.WorkflowReader.readWorkflowFromClasspath;
 import static org.assertj.core.api.Assertions.assertThat;
 
+import io.serverlessworkflow.api.types.CallFunction;
 import io.serverlessworkflow.api.types.CallHTTP;
 import io.serverlessworkflow.api.types.CallTask;
 import io.serverlessworkflow.api.types.Task;
@@ -27,6 +28,24 @@
 
 public class ApiTest {
 
+  @Test
+  void testCallFunctionAPIWithoutArguments() throws IOException {
+    Workflow workflow = readWorkflowFromClasspath("features/callFunction.yaml");
+    assertThat(workflow.getDo()).isNotEmpty();
+    assertThat(workflow.getDo().get(0).getName()).isNotNull();
+    assertThat(workflow.getDo().get(0).getTask()).isNotNull();
+    Task task = workflow.getDo().get(0).getTask();
+    CallTask callTask = task.getCallTask();
+    assertThat(callTask).isNotNull();
+    assertThat(callTask.get()).isInstanceOf(CallFunction.class);
+    if (callTask.get() instanceof CallFunction) {
+      CallFunction functionCall = callTask.getCallFunction();
+      assertThat(functionCall).isNotNull();
+      assertThat(callTask.getCallAsyncAPI()).isNull();
+      assertThat(functionCall.getWith()).isNull();
+    }
+  }
+
   @Test
   void testCallHTTPAPI() throws IOException {
     Workflow workflow = readWorkflowFromClasspath("features/callHttp.yaml");
diff --git a/api/src/test/resources/features/callFunction.yaml b/api/src/test/resources/features/callFunction.yaml
new file mode 100644
index 00000000..695ad25c
--- /dev/null
+++ b/api/src/test/resources/features/callFunction.yaml
@@ -0,0 +1,18 @@
+document:
+  dsl: 1.0.0-alpha1
+  namespace: default
+  name: http-call-with-response-output
+
+use:
+  functions:
+    getPet:
+      call: http
+      with:
+        method: get
+        endpoint:
+          uri: https://petstore.swagger.io/v2/pet/{petId}
+        output: response
+
+do:
+  - getPetFunctionCall:
+      call: getPet