diff --git a/pre_commit_hooks/pretty_format_json.py b/pre_commit_hooks/pretty_format_json.py
index 605cbec..36a90eb 100644
--- a/pre_commit_hooks/pretty_format_json.py
+++ b/pre_commit_hooks/pretty_format_json.py
@@ -28,19 +28,20 @@
     # type: (str) -> str
     try:
         int_indentation_spec = int(s)
+    except ValueError:
+        if not s.strip():
+            return s
+        else:
+            raise ValueError(
+                'Non-whitespace JSON indentation delimiter supplied. ',
+            )
+    else:
         if int_indentation_spec >= 0:
             return int_indentation_spec * ' '
         else:
             raise ValueError(
                 'Negative integer supplied to construct JSON indentation delimiter. ',
             )
-    except ValueError:
-        if s.strip() == '':
-            return s
-        else:
-            raise ValueError(
-                'Non-whitespace JSON indentation delimiter supplied. ',
-            )
 
 
 def pretty_format_json(argv=None):