diff --git a/moto/dynamodb2/models.py b/moto/dynamodb2/models.py
index b327c7a4b..0fa96f3b6 100644
--- a/moto/dynamodb2/models.py
+++ b/moto/dynamodb2/models.py
@@ -154,7 +154,7 @@ class Item(BaseModel):
                     # If not exists, changes value to a default if needed, else its the same as it was
                     if value.startswith('if_not_exists'):
                         # Function signature
-                        match = re.match(r'.*if_not_exists\((?P<path>.+),\s*(?P<default>.+)\).*', value)
+                        match = re.match(r'.*if_not_exists\s*\((?P<path>.+),\s*(?P<default>.+)\).*', value)
                         if not match:
                             raise TypeError
 
diff --git a/tests/test_dynamodb2/test_dynamodb.py b/tests/test_dynamodb2/test_dynamodb.py
index 243de2701..70feaf7f6 100644
--- a/tests/test_dynamodb2/test_dynamodb.py
+++ b/tests/test_dynamodb2/test_dynamodb.py
@@ -1220,7 +1220,8 @@ def test_update_if_not_exists():
         'forum_name': 'the-key',
         'subject': '123'
         },
-        UpdateExpression='SET created_at = if_not_exists(created_at, :created_at)',
+        # if_not_exists without space
+        UpdateExpression='SET created_at=if_not_exists(created_at,:created_at)',
         ExpressionAttributeValues={
             ':created_at': 123
         }
@@ -1233,7 +1234,8 @@ def test_update_if_not_exists():
         'forum_name': 'the-key',
         'subject': '123'
         },
-        UpdateExpression='SET created_at = if_not_exists(created_at, :created_at)',
+        # if_not_exists with space
+        UpdateExpression='SET created_at = if_not_exists (created_at, :created_at)',
         ExpressionAttributeValues={
             ':created_at': 456
         }