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 39af1118cfc..2e8b0ebab5b 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
@@ -3035,6 +3035,8 @@ public class DefaultCodegen {
         word = word.replaceAll(firstPattern, replacementPattern);
         word = word.replaceAll(secondPattern, replacementPattern);
         word = word.replace('-', '_');
+        // replace space with underscore
+        word = word.replace(' ', '_');
         word = word.toLowerCase();
         return word;
     }
diff --git a/modules/swagger-codegen/src/test/java/io/swagger/codegen/CodegenTest.java b/modules/swagger-codegen/src/test/java/io/swagger/codegen/CodegenTest.java
index 18acd4757a9..0fae4eac112 100644
--- a/modules/swagger-codegen/src/test/java/io/swagger/codegen/CodegenTest.java
+++ b/modules/swagger-codegen/src/test/java/io/swagger/codegen/CodegenTest.java
@@ -25,6 +25,18 @@ public class CodegenTest {
         Assert.assertEquals(codegen.sanitizeTag("1foo"), "Class1foo");
     }
 
+    @Test(description = "test underscore")
+    public void underscoreNamesTest() {
+        final DefaultCodegen codegen = new DefaultCodegen();
+
+        Assert.assertEquals(codegen.underscore("foo"), "foo");
+        Assert.assertEquals(codegen.underscore("foo-bar"), "foo_bar");
+        Assert.assertEquals(codegen.underscore("foo bar"), "foo_bar");
+
+        Assert.assertEquals(codegen.underscore("FooBar"), "foo_bar");
+        Assert.assertEquals(codegen.underscore("FooBarBaz"), "foo_bar_baz");
+    }
+
     @Test(description = "test camelize")
     public void camelizeNamesTest() {
         final DefaultCodegen codegen = new DefaultCodegen();