diff --git a/dlls/advapi32/service.c b/dlls/advapi32/service.c
index 050efc85bc7..a107397e658 100644
--- a/dlls/advapi32/service.c
+++ b/dlls/advapi32/service.c
@@ -1680,6 +1680,7 @@ BOOL WINAPI GetServiceDisplayNameW( SC_HANDLE hSCManager, LPCWSTR lpServiceName,
   LPWSTR lpDisplayName, LPDWORD lpcchBuffer)
 {
     DWORD err;
+    WCHAR buffer[2];
 
     TRACE("%p %s %p %p\n", hSCManager,
           debugstr_w(lpServiceName), lpDisplayName, lpcchBuffer);
@@ -1690,10 +1691,20 @@ BOOL WINAPI GetServiceDisplayNameW( SC_HANDLE hSCManager, LPCWSTR lpServiceName,
         return 0;
     }
 
+    /* provide a buffer if the caller didn't */
+    if (!lpDisplayName || *lpcchBuffer < 2)
+    {
+        lpDisplayName = buffer;
+        /* A size of 1 would be enough, but tests show that Windows returns 2,
+         * probably because of a WCHAR/bytes mismatch in their code.
+         */
+        *lpcchBuffer = 2;
+    }
+
     __TRY
     {
         err = svcctl_GetServiceDisplayNameW(hSCManager, lpServiceName, lpDisplayName,
-                                            lpDisplayName ? *lpcchBuffer : 0, lpcchBuffer);
+                                            *lpcchBuffer, lpcchBuffer);
     }
     __EXCEPT(rpc_filter)
     {
diff --git a/dlls/advapi32/tests/service.c b/dlls/advapi32/tests/service.c
index 625aff3be3e..451a21be087 100644
--- a/dlls/advapi32/tests/service.c
+++ b/dlls/advapi32/tests/service.c
@@ -476,7 +476,7 @@ static void test_get_displayname(void)
     ok(!ret, "Expected failure\n");
     ok(GetLastError() == ERROR_SERVICE_DOES_NOT_EXIST,
        "Expected ERROR_SERVICE_DOES_NOT_EXIST, got %d\n", GetLastError());
-    todo_wine ok(displaysize == 15, "Service size expected 15, got %d\n", displaysize);
+    ok(displaysize == 15, "Service size expected 15, got %d\n", displaysize);
     ok(displaynameW[0] == 0, "Service name not empty\n");
 
     displaysize = 0;
@@ -492,7 +492,7 @@ static void test_get_displayname(void)
     lstrcpyW( displaynameW, abcW );
     ret = GetServiceDisplayNameW(scm_handle, deadbeefW, displaynameW, &displaysize);
     ok(!ret, "Expected failure\n");
-    todo_wine ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
+    ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
     ok(GetLastError() == ERROR_SERVICE_DOES_NOT_EXIST,
        "Expected ERROR_SERVICE_DOES_NOT_EXIST, got %d\n", GetLastError());
     ok(displaynameW[0] == 'A', "Service name changed\n");
@@ -510,10 +510,10 @@ static void test_get_displayname(void)
     lstrcpyW( displaynameW, abcW );
     ret = GetServiceDisplayNameW(scm_handle, deadbeefW, displaynameW, &displaysize);
     ok(!ret, "Expected failure\n");
-    todo_wine ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
+    ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
     ok(GetLastError() == ERROR_SERVICE_DOES_NOT_EXIST,
        "Expected ERROR_SERVICE_DOES_NOT_EXIST, got %d\n", GetLastError());
-    todo_wine ok(displaynameW[0] == 'A', "Service name changed\n");
+    ok(displaynameW[0] == 'A', "Service name changed\n");
 
     displaysize = 2;
     strcpy(displayname, "ABC");
@@ -521,14 +521,14 @@ static void test_get_displayname(void)
     ok(!ret, "Expected failure\n");
     ok(GetLastError() == ERROR_SERVICE_DOES_NOT_EXIST,
        "Expected ERROR_SERVICE_DOES_NOT_EXIST, got %d\n", GetLastError());
-    ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
+    todo_wine ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
     ok(displayname[0] == 0, "Service name not empty\n");
 
     displaysize = 2;
     lstrcpyW( displaynameW, abcW );
     ret = GetServiceDisplayNameW(scm_handle, deadbeefW, displaynameW, &displaysize);
     ok(!ret, "Expected failure\n");
-    todo_wine ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
+    ok(displaysize == 2, "Service size expected 2, got %d\n", displaysize);
     ok(GetLastError() == ERROR_SERVICE_DOES_NOT_EXIST,
        "Expected ERROR_SERVICE_DOES_NOT_EXIST, got %d\n", GetLastError());
     ok(displaynameW[0] == 0, "Service name not empty\n");
diff --git a/include/wine/svcctl.idl b/include/wine/svcctl.idl
index 918c80eb679..36bf476e04e 100644
--- a/include/wine/svcctl.idl
+++ b/include/wine/svcctl.idl
@@ -232,7 +232,7 @@ typedef [switch_type(DWORD)] union
         [in] LPCWSTR lpServiceName,
         [out,size_is(cchBufSize)] WCHAR lpBuffer[],
         [in] DWORD cchBufSize,
-        [out] DWORD *cchLength);
+        [in,out] DWORD *cchLength);
 
     /* Compatible with Windows function 0x15 */
     DWORD svcctl_GetServiceKeyNameW(
diff --git a/programs/services/rpc.c b/programs/services/rpc.c
index d88e148fdcd..cbb825e2cc9 100644
--- a/programs/services/rpc.c
+++ b/programs/services/rpc.c
@@ -215,10 +215,7 @@ DWORD svcctl_GetServiceDisplayNameW(
         service_unlock(entry);
     }
     else
-    {
-        *cchLength = 1;
         err = ERROR_SERVICE_DOES_NOT_EXIST;
-    }
 
     scmdatabase_unlock(manager->db);