diff --git a/src/opengnsys/RESTApi.py b/src/opengnsys/RESTApi.py
index 8773cf5..3e3468f 100644
--- a/src/opengnsys/RESTApi.py
+++ b/src/opengnsys/RESTApi.py
@@ -142,6 +142,10 @@ class REST(object):
                 else:
                     r = requests.post(url, data=data, headers={'content-type': 'application/json'})
 
+            r.raise_for_status()
+            ct = r.headers['Content-Type']
+            if 'application/json' != ct:
+                raise Exception (f'response content-type is not "application/json" but "{ct}"')
             r = json.loads(r.content)  # Using instead of r.json() to make compatible with old requests lib versions
         except requests.exceptions.RequestException as e:
             raise ConnectionError(e)