diff --git a/services/src/main/java/edu/msudenver/tsp/services/DefinitionService.java b/services/src/main/java/edu/msudenver/tsp/services/DefinitionService.java
index 6ffa013..e8ec3a2 100644
--- a/services/src/main/java/edu/msudenver/tsp/services/DefinitionService.java
+++ b/services/src/main/java/edu/msudenver/tsp/services/DefinitionService.java
@@ -117,6 +117,11 @@ public class DefinitionService {
             return Optional.empty();
         }
 
+        if (definition.getId() == 0) {
+            LOG.error("Given invalid id 0, returning {}");
+            return Optional.empty();
+        }
+
         LOG.info("Sending request to update definition {}", definition);
         final Instant start = Instant.now();
 
diff --git a/services/src/test/java/edu/msudenver/tsp/services/DefinitionServiceTest.java b/services/src/test/java/edu/msudenver/tsp/services/DefinitionServiceTest.java
index 0631854..e7b423f 100644
--- a/services/src/test/java/edu/msudenver/tsp/services/DefinitionServiceTest.java
+++ b/services/src/test/java/edu/msudenver/tsp/services/DefinitionServiceTest.java
@@ -43,7 +43,7 @@ public class DefinitionServiceTest {
     }
 
     @Test
-    public void testGetAllDefinitions_ReturnsEmptyOptional() {
+    public void testGetAllDefinitions_RequestReturnsEmptyOptional() {
         when(restService.get(anyString(), any(), anyInt(), anyInt(), anyString()))
                 .thenReturn(Optional.empty());
 
@@ -79,7 +79,7 @@ public class DefinitionServiceTest {
     }
 
     @Test
-    public void testFindById_ReturnsEmptyOptional() {
+    public void testFindById_RequestReturnsEmptyOptional() {
         when(restService.get(anyString(), any(), anyInt(), anyInt(), anyString()))
                 .thenReturn(Optional.empty());
 
@@ -125,7 +125,7 @@ public class DefinitionServiceTest {
     }
 
     @Test
-    public void testCreateDefinition_unableToCreateDefinition() {
+    public void testCreateDefinition_UnableToCreateDefinition() {
         final Definition testDefinition = createDefinition();
         final String testDefinitionJson = new GsonBuilder().create().toJson(testDefinition);
 
@@ -140,7 +140,7 @@ public class DefinitionServiceTest {
     }
 
     @Test
-    public void testCreateDefinition_restServiceThrowsException() {
+    public void testCreateDefinition_RestServiceThrowsException() {
         final Definition testDefinition = createDefinition();
         final String testDefinitionJson = new GsonBuilder().create().toJson(testDefinition);
 
@@ -154,6 +154,64 @@ public class DefinitionServiceTest {
         verify(restService).post(anyString(), eq(testDefinitionJson), any(), anyInt(), anyInt());
     }
 
+    @Test
+    public void testUpdateDefinition() {
+        when(restService.patch(anyString(), anyString(), any(), anyInt(), anyInt()))
+                .thenReturn(Optional.of(createDefinition().setName("Test update")));
+
+        final Definition testDefinition = new Definition();
+        testDefinition.setName("Test update");
+        testDefinition.setId(1);
+
+        final Optional<Definition> updatedDefinition = definitionService.updateDefinition(testDefinition);
+
+        assertTrue(updatedDefinition.isPresent());
+        assertThat(updatedDefinition.get().getId(), is(1));
+        assertThat(updatedDefinition.get().getName(), is(equalTo("Test update")));
+        verify(restService).patch(anyString(), anyString(), any(), anyInt(), anyInt());
+    }
+
+    @Test
+    public void testUpdateDefinition_nullDefinition() {
+        final Optional<Definition> testUpdate = definitionService.updateDefinition(null);
+
+        assertFalse(testUpdate.isPresent());
+        verifyZeroInteractions(restService);
+    }
+
+    @Test
+    public void testUpdateDefinition_IdIsZero() {
+        final Definition impossibleDefinition = createDefinition();
+        impossibleDefinition.setId(0);
+
+        final Optional<Definition> testUpdate = definitionService.updateDefinition(impossibleDefinition);
+
+        assertFalse(testUpdate.isPresent());
+        verifyZeroInteractions(restService);
+    }
+
+    @Test
+    public void testUpdateDefinition_RequestReturnsEmptyOptional() {
+        when(restService.patch(anyString(), anyString(), any(), anyInt(), anyInt()))
+                .thenReturn(Optional.empty());
+
+        final Optional<Definition> nonExistentDefinition = definitionService.updateDefinition(createDefinition());
+
+        assertFalse(nonExistentDefinition.isPresent());
+        verify(restService).patch(anyString(), anyString(), any(), anyInt(), anyInt());
+    }
+
+    @Test
+    public void testUpdateDefinition_ExceptionThrownWhenSendingRequest() {
+        when(restService.patch(anyString(), anyString(), any(), anyInt(), anyInt()))
+                .thenThrow(new UnsupportedOperationException("test exception"));
+
+        final Optional<Definition> exceptionThrowingDefinition = definitionService.updateDefinition(createDefinition());
+
+        assertFalse(exceptionThrowingDefinition.isPresent());
+        verify(restService).patch(anyString(), anyString(), any(), anyInt(), anyInt());
+    }
+
     private Definition createDefinition() {
         final List<String> definitionList = new ArrayList<>();
         definitionList.add("Test definition 1");