diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
index 32947d78706..a9780140f4c 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
@@ -3170,10 +3170,16 @@ public class DefaultCodegen implements CodegenConfig {
         List<MappedModel> uniqueDescendants = new ArrayList();
         if (sourceDiscriminator.getMapping() != null && !sourceDiscriminator.getMapping().isEmpty()) {
             for (Entry<String, String> e : sourceDiscriminator.getMapping().entrySet()) {
-                String nameOrRef = e.getValue();
-                String name = nameOrRef.indexOf('/') >= 0 ? ModelUtils.getSimpleRef(nameOrRef) : nameOrRef;
-                String modelName = toModelName(name);
-                uniqueDescendants.add(new MappedModel(e.getKey(), modelName));
+                String name;
+                if (e.getValue().indexOf('/') >= 0) {
+                    name = ModelUtils.getSimpleRef(e.getValue());
+                    if (ModelUtils.getSchema(openAPI, name) == null) {
+                        LOGGER.error("Failed to lookup the schema '{}' when processing the discriminator mapping of oneOf/anyOf. Please check to ensure it's defined properly.", name);
+                    }
+                } else {
+                    name = e.getValue();
+                }
+                uniqueDescendants.add(new MappedModel(e.getKey(), toModelName(name)));
             }
         }