diff --git a/src/core/base/ThingThatCanBeOffered.ts b/src/core/base/ThingThatCanBeOffered.ts
index 21c2332c..56ccb111 100644
--- a/src/core/base/ThingThatCanBeOffered.ts
+++ b/src/core/base/ThingThatCanBeOffered.ts
@@ -20,10 +20,13 @@ import {SCISO8601Date} from '../types/Time';
 import {SCInPlace} from './../types/Places';
 
 /**
- * A map from group name to price
+ * Default price without distinction
  */
 export interface SCPriceGroup {
-  [s: string]: number | undefined;
+  /**
+   * Default price of the thing
+   */
+  default: number;
 }
 
 /**
@@ -82,15 +85,10 @@ export interface SCThingThatCanBeOfferedOffer<T extends SCPriceGroup>
    */
   availabilityStarts?: SCISO8601Date;
 
-  /**
-   * Default price of the thing
-   */
-  price: number;
-
   /**
    * List of prices that are distinct for specific groups
    */
-  prices?: T;
+  prices: T;
 
   /**
    * Provider of an offer
diff --git a/src/core/things/DateSeries.ts b/src/core/things/DateSeries.ts
index 36b9df59..5eb15aee 100644
--- a/src/core/things/DateSeries.ts
+++ b/src/core/things/DateSeries.ts
@@ -32,7 +32,7 @@ export interface SCSportCoursePriceGroup extends SCAcademicPriceGroup {
   /**
    * Price for alumnis
    */
-  alumni: number;
+  alumni?: number;
 }
 
 /**
diff --git a/test/resources/DateSeries.3.json b/test/resources/DateSeries.3.json
new file mode 100644
index 00000000..c4556164
--- /dev/null
+++ b/test/resources/DateSeries.3.json
@@ -0,0 +1,77 @@
+{
+  "errorNames": [],
+  "instance":  {
+    "type": "date series",
+    "uid": "540862f3-ea30-5b8f-8678-56b4dc217140",
+    "name": "Dance course for beginners",
+    "duration": "PT8H",
+    "inPlace": {
+      "geo": {
+        "point": {
+          "type": "Point",
+          "coordinates": [
+            13.3266207,
+            52.5144409
+          ]
+        }
+      },
+      "type": "room",
+      "categories": [
+        "student union"
+      ],
+      "uid": "540862f3-ea30-5b8f-8678-56b4dc217140",
+      "name": "EMH 225",
+      "floor": "2",
+      "origin": {
+        "indexed": "2018-09-11T12:30:00Z",
+        "name": "Dummy",
+        "type": "remote"
+      }
+    },
+    "frequency": "once",
+    "dates": [
+      "2016-04-12T11:00:00+00:00"
+    ],
+    "event": {
+      "type": "academic event",
+      "uid": "540862f3-ea30-5b8f-8678-56b4dc217140",
+      "name": "Dance course for beginners",
+      "categories": [
+        "special"
+      ],
+      "origin": {
+        "indexed": "2018-09-11T12:30:00Z",
+        "name": "Dummy",
+        "type": "remote"
+      }
+    },
+    "origin": {
+      "indexed": "2018-09-11T12:30:00Z",
+      "name": "Dummy",
+      "type": "remote"
+    },
+        "offers": [
+      {
+        "availability": "in stock",
+        "availabilityStarts": "2017-01-30T00:00:00.000Z",
+        "availabilityEnds": "2017-01-30T23:59:59.999Z",
+        "prices": {
+          "default": 6.5,
+          "student": 5,
+          "alumni": 5
+        },
+        "provider": {
+          "name": "Studentenwerk",
+          "origin": {
+            "indexed": "2018-09-11T12:30:00Z",
+            "name": "Dummy",
+            "type": "remote"
+          }, 
+          "type": "organization",
+          "uid": "3b9b3df6-3a7a-58cc-922f-c7335c002634"
+        }
+      }
+    ]
+  },
+  "schema": "SCDateSeries"
+}
diff --git a/test/resources/Dish.1.json b/test/resources/Dish.1.json
index 9b1e4709..44d88bee 100644
--- a/test/resources/Dish.1.json
+++ b/test/resources/Dish.1.json
@@ -21,10 +21,11 @@
         "availability": "in stock",
         "availabilityStarts": "2017-01-30T00:00:00.000Z",
         "availabilityEnds": "2017-01-30T23:59:59.999Z",
-        "price": 2.85,
         "prices": {
+          "default": 4.85,
           "student": 2.85,
-          "employee": 2.85
+          "employee": 3.85,
+          "guest": 4.85
         },
         "provider": {
           "name": "Studentenwerk",
diff --git a/test/resources/Dish.2.json b/test/resources/Dish.2.json
index 8d697851..7d7f57c8 100644
--- a/test/resources/Dish.2.json
+++ b/test/resources/Dish.2.json
@@ -9,10 +9,10 @@
     ],
     "offers": [
       {
-        "price": 2.45,
         "prices": {
+          "default": 3.45,
           "student": 2.45,
-          "employee": 2.45
+          "employee": 3.45
         },
         "provider": {
           "name": "Studentenwerk",
diff --git a/test/resources/Dish.3.json b/test/resources/Dish.3.json
index 992e570b..1001e127 100644
--- a/test/resources/Dish.3.json
+++ b/test/resources/Dish.3.json
@@ -41,10 +41,10 @@
           }
         },
         "prices": {
+          "default": 6.5,
           "student": 4.9,
           "employee": 6.5
         },
-        "price": 6.5,
         "provider": {
           "name": "Studentenwerk",
           "origin": {