diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
index 5ea4a08a1a34..11691abbedb7 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
@@ -19,6 +19,7 @@
 
 import io.swagger.v3.core.util.Json;
 import io.swagger.v3.oas.models.*;
+import io.swagger.v3.oas.models.callbacks.Callback;
 import io.swagger.v3.oas.models.media.*;
 import io.swagger.v3.oas.models.parameters.Parameter;
 import io.swagger.v3.oas.models.parameters.RequestBody;
@@ -29,6 +30,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.util.*;
+import java.util.stream.Collectors;
 
 public class InlineModelResolver {
     private OpenAPI openapi;
@@ -64,7 +66,20 @@ private void flattenPaths(OpenAPI openAPI) {
 
         for (String pathname : paths.keySet()) {
             PathItem path = paths.get(pathname);
+            List<Operation> operations = new ArrayList<>(path.readOperations());
+
+            // Include callback operation as well
             for (Operation operation : path.readOperations()) {
+                Map<String, Callback> callbacks = operation.getCallbacks();
+                if (callbacks != null) {
+                    operations.addAll(callbacks.values().stream()
+                            .flatMap(callback -> callback.values().stream())
+                            .flatMap(pathItem -> pathItem.readOperations().stream())
+                            .collect(Collectors.toList()));
+                }
+            }
+
+            for (Operation operation : operations) {
                 flattenRequestBody(openAPI, pathname, operation);
                 flattenParameters(openAPI, pathname, operation);
                 flattenResponses(openAPI, pathname, operation);