diff --git a/modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultCodegen.java b/modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultCodegen.java
index 61a4dc1ba61..3999ae6ac5e 100644
--- a/modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultCodegen.java
+++ b/modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultCodegen.java
@@ -119,7 +119,7 @@ public class DefaultCodegen {
     // Then translated back during JSON encoding and decoding
     protected Map<String, String> specialCharReplacements = new HashMap<String, String>();
     // When a model is an alias for a simple type
-    protected Map<String, String> typeAliases = new HashMap<>();
+    protected Map<String, String> typeAliases = null;
 
     protected String ignoreFilePathOverride;
 
@@ -1312,6 +1312,10 @@ public CodegenModel fromModel(String name, Model model) {
      * @return Codegen Model object
      */
     public CodegenModel fromModel(String name, Model model, Map<String, Model> allDefinitions) {
+        if (typeAliases == null) {
+            // Only do this once during first call
+            typeAliases = getAllAliases(allDefinitions);
+        }
         CodegenModel m = CodegenModelFactory.newInstance(CodegenModelType.MODEL);
         if (reservedWords.contains(name)) {
             m.name = escapeReservedWord(name);
@@ -1327,6 +1331,7 @@ public CodegenModel fromModel(String name, Model model, Map<String, Model> allDe
         m.modelJson = Json.pretty(model);
         m.externalDocs = model.getExternalDocs();
         m.vendorExtensions = model.getVendorExtensions();
+        m.isAlias = typeAliases.containsKey(name);
 
         if (model instanceof ModelImpl) {
           ModelImpl modelImpl = (ModelImpl) model;
@@ -1444,10 +1449,6 @@ public CodegenModel fromModel(String name, Model model, Map<String, Model> allDe
             ModelImpl impl = (ModelImpl) model;
             if (impl.getType() != null) {
                 Property p = PropertyBuilder.build(impl.getType(), impl.getFormat(), null);
-                if (!impl.getType().equals("object") && impl.getEnum() == null) {
-                    typeAliases.put(name, impl.getType());
-                    m.isAlias = true;
-                }
                 m.dataType = getSwaggerType(p);
             }
             if(impl.getEnum() != null && impl.getEnum().size() > 0) {
@@ -3166,6 +3167,31 @@ private void addVars(CodegenModel m, List<CodegenProperty> vars, Map<String, Pro
         }
     }
 
+    /**
+     * Determine all of the types in the model definitions that are aliases of
+     * simple types.
+     * @param allDefinitions The complete set of model definitions.
+     * @return A mapping from model name to type alias
+     */
+    private static Map<String, String> getAllAliases(Map<String, Model> allDefinitions) {
+        Map<String, String> aliases = new HashMap<>();
+        if (allDefinitions != null) {
+            for (Map.Entry<String, Model> entry : allDefinitions.entrySet()) {
+                String swaggerName = entry.getKey();
+                Model m = entry.getValue();
+                if (m instanceof ModelImpl) {
+                    ModelImpl impl = (ModelImpl) m;
+                    if (impl.getType() != null &&
+                            !impl.getType().equals("object") &&
+                            impl.getEnum() == null) {
+                        aliases.put(swaggerName, impl.getType());
+                    }
+                }
+            }
+        }
+        return aliases;
+    }
+
     /**
      * Remove characters not suitable for variable or method name from the input and camelize it
      *
diff --git a/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractJavaCodegen.java b/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractJavaCodegen.java
index 13310ecc5c3..2d471bf6207 100644
--- a/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractJavaCodegen.java
+++ b/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractJavaCodegen.java
@@ -619,7 +619,7 @@ public String getTypeDeclaration(Property p) {
 
     @Override
     public String getAlias(String name) {
-        if (typeAliases.containsKey(name)) {
+        if (typeAliases != null && typeAliases.containsKey(name)) {
             return typeAliases.get(name);
         }
         return name;
diff --git a/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml b/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
index 19db9dcbf51..059a5ef4980 100644
--- a/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
+++ b/modules/swagger-codegen/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
@@ -1402,12 +1402,6 @@ definitions:
     - "placed"
     - "approved"
     - "delivered"
-  OuterNumber:
-    type: number
-  OuterString:
-    type: string
-  OuterBoolean:
-    type: boolean
   OuterComposite:
     type: object
     properties:
@@ -1417,6 +1411,12 @@ definitions:
         $ref: '#/definitions/OuterString'
       my_boolean:
         $ref: '#/definitions/OuterBoolean'
+  OuterNumber:
+    type: number
+  OuterString:
+    type: string
+  OuterBoolean:
+    type: boolean
 externalDocs:
   description: Find out more about Swagger
   url: 'http://swagger.io'