diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
index f6623fe0..82f6cdf0 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
@@ -113,7 +113,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                         "debitorNumber": 1000111,
                         "debitorNumberSuffix": "11",
                         "partner": {
-                          "partnerNumber": 10001,
+                          "partnerNumber": "P-10001",
                           "partnerRel": {
                             "anchor": {
                               "personType": "LEGAL_PERSON",
@@ -168,7 +168,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                         "debitorNumber": 1000212,
                         "debitorNumberSuffix": "12",
                         "partner": {
-                          "partnerNumber": 10002,
+                          "partnerNumber": "P-10002",
                           "partnerRel": {
                             "anchor": {"tradeName": "Hostsharing eG"},
                             "holder": {"tradeName": "Second e.K."},
@@ -202,7 +202,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                         "debitorNumber": 1000313,
                         "debitorNumberSuffix": "13",
                         "partner": {
-                          "partnerNumber": 10003,
+                          "partnerNumber": "P-10003",
                           "partnerRel": {
                             "anchor": {"tradeName": "Hostsharing eG"},
                             "holder": {"tradeName": "Third OHG"},
@@ -245,7 +245,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                      [
                          {
                              "debitorNumber": 1000212,
-                             "partner": { "partnerNumber": 10002 },
+                             "partner": { "partnerNumber": "P-10002" },
                              "debitorRel": {
                                 "contact": { "caption": "second contact" }
                              },
@@ -535,7 +535,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                     .body("", lenientlyEquals("""
                     {
                         "debitorNumber": 1000111,
-                        "partner": { "partnerNumber": 10001 },
+                        "partner": { "partnerNumber": "P-10001" },
                         "debitorRel": { "contact": { "caption": "first contact" } },
                         "refundBankAccount": null
                     }
@@ -584,7 +584,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                                 "debitorNumber": 10004${debitorNumberSuffix},
                                 "debitorNumberSuffix": "${debitorNumberSuffix}",
                                 "partner": {
-                                    "partnerNumber": 10004,
+                                    "partnerNumber": "P-10004",
                                     "partnerRel": {
                                         "anchor": { "tradeName": "Hostsharing eG" },
                                         "holder": { "tradeName": "Fourth eG" },
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerAcceptanceTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerAcceptanceTest.java
index f3793da1..33073956 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerAcceptanceTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerAcceptanceTest.java
@@ -77,7 +77,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                     .body("", lenientlyEquals("""
                       [
                           {
-                              "partner": { "partnerNumber": 10001 },
+                              "partner": { "partnerNumber": "P-10001" },
                               "memberNumber": 1000101,
                               "memberNumberSuffix": "01",
                               "validFrom": "2022-10-01",
@@ -85,7 +85,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                               "status": "ACTIVE"
                           },
                           {
-                              "partner": { "partnerNumber": 10002 },
+                              "partner": { "partnerNumber": "P-10002" },
                               "memberNumber": 1000202,
                               "memberNumberSuffix": "02",
                               "validFrom": "2022-10-01",
@@ -93,7 +93,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                               "status": "ACTIVE"
                           },
                           {
-                              "partner": { "partnerNumber": 10003 },
+                              "partner": { "partnerNumber": "P-10003" },
                               "memberNumber": 1000303,
                               "memberNumberSuffix": "03",
                               "validFrom": "2022-10-01",
@@ -124,7 +124,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                     .body("", lenientlyEquals("""
                       [
                           {
-                              "partner": { "partnerNumber": 10001 },
+                              "partner": { "partnerNumber": "P-10001" },
                               "memberNumber": 1000101,
                               "memberNumberSuffix": "01",
                               "validFrom": "2022-10-01",
@@ -152,7 +152,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                     .body("", lenientlyEquals("""
                       [
                           {
-                              "partner": { "partnerNumber": 10002 },
+                              "partner": { "partnerNumber": "P-10002" },
                               "memberNumber": 1000202,
                               "memberNumberSuffix": "02",
                               "validFrom": "2022-10-01",
@@ -195,7 +195,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                         .statusCode(201)
                         .contentType(ContentType.JSON)
                         .body("uuid", isUuidValid())
-                        .body("partner.partnerNumber", is(10003))
+                        .body("partner.partnerNumber", is("P-10003"))
                         .body("memberNumber", is(expectedMemberNumber))
                         .body("memberNumberSuffix", is(givenMemberSuffix))
                         .body("validFrom", is("2022-10-13"))
@@ -230,7 +230,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                     .contentType("application/json")
                     .body("", lenientlyEquals("""
                     {
-                         "partner": { "partnerNumber": 10001 },
+                         "partner": { "partnerNumber": "P-10001" },
                          "memberNumber": 1000101,
                          "memberNumberSuffix": "01",
                          "validFrom": "2022-10-01",
@@ -272,7 +272,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                     .contentType("application/json")
                     .body("", lenientlyEquals("""
                     {
-                         "partner": { "partnerNumber": 10003 },
+                         "partner": { "partnerNumber": "P-10003" },
                          "memberNumber": 1000303,
                          "memberNumberSuffix": "03",
                          "validFrom": "2022-10-01",
@@ -309,7 +309,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
                     .statusCode(200)
                     .contentType(ContentType.JSON)
                     .body("uuid", isUuidValid())
-                    .body("partner.partnerNumber", is(givenMembership.getPartner().getPartnerNumber()))
+                    .body("partner.partnerNumber", is("P-" + givenMembership.getPartner().getPartnerNumber()))
                     .body("memberNumberSuffix", is(givenMembership.getMemberNumberSuffix()))
                     .body("validFrom", is("2022-11-01"))
                     .body("validTo", is("2023-12-31"))