diff --git a/src/fsfw/pus/Service11TelecommandScheduling.h b/src/fsfw/pus/Service11TelecommandScheduling.h
index 2a14401b..57ba4982 100644
--- a/src/fsfw/pus/Service11TelecommandScheduling.h
+++ b/src/fsfw/pus/Service11TelecommandScheduling.h
@@ -38,8 +38,9 @@ class Service11TelecommandScheduling final : public PusServiceBase {
   static constexpr uint8_t CLASS_ID = CLASS_ID::PUS_SERVICE_11;
 
   static constexpr ReturnValue_t INVALID_TYPE_TIME_WINDOW = returnvalue::makeCode(CLASS_ID, 1);
-  static constexpr ReturnValue_t TIMESHIFTING_NOT_POSSIBLE = returnvalue::makeCode(CLASS_ID, 2);
-  static constexpr ReturnValue_t INVALID_RELATIVE_TIME = returnvalue::makeCode(CLASS_ID, 3);
+  static constexpr ReturnValue_t INVALID_TIME_WINDOW = returnvalue::makeCode(CLASS_ID, 2);
+  static constexpr ReturnValue_t TIMESHIFTING_NOT_POSSIBLE = returnvalue::makeCode(CLASS_ID, 3);
+  static constexpr ReturnValue_t INVALID_RELATIVE_TIME = returnvalue::makeCode(CLASS_ID, 4);
 
   static constexpr uint8_t SUBSYSTEM_ID = SUBSYSTEM_ID::PUS_SERVICE_11;
 
diff --git a/src/fsfw/pus/Service11TelecommandScheduling.tpp b/src/fsfw/pus/Service11TelecommandScheduling.tpp
index 7f60f7e8..c82c1703 100644
--- a/src/fsfw/pus/Service11TelecommandScheduling.tpp
+++ b/src/fsfw/pus/Service11TelecommandScheduling.tpp
@@ -571,12 +571,17 @@ inline ReturnValue_t Service11TelecommandScheduling<MAX_NUM_TCS>::getMapFilterFr
       if (result != returnvalue::OK) {
         return result;
       }
+      if(fromTimestamp > toTimestamp) {
+        return INVALID_TIME_WINDOW;
+      }
       itBegin = telecommandMap.begin();
-      itEnd = telecommandMap.begin();
 
       while (itBegin->first < fromTimestamp && itBegin != telecommandMap.end()) {
         itBegin++;
       }
+
+      //start looking for end beginning at begin
+      itEnd = itBegin;
       while (itEnd->first <= toTimestamp && itEnd != telecommandMap.end()) {
         itEnd++;
       }
@@ -586,17 +591,6 @@ inline ReturnValue_t Service11TelecommandScheduling<MAX_NUM_TCS>::getMapFilterFr
     default:
       return returnvalue::FAILED;
   }
-
-  // additional security check, this should never be true
-  if (itBegin > itEnd) {
-#if FSFW_CPP_OSTREAM_ENABLED == 1
-    sif::error << "11::getMapFilterFromData: itBegin > itEnd\n" << std::endl;
-#else
-    sif::printError("11::getMapFilterFromData: itBegin > itEnd\n");
-#endif
-    return returnvalue::FAILED;
-  }
-
   // the map range should now be set according to the sent filter.
   return returnvalue::OK;
 }
diff --git a/unittests/CMakeLists.txt b/unittests/CMakeLists.txt
index 8c7f2463..d7c35975 100644
--- a/unittests/CMakeLists.txt
+++ b/unittests/CMakeLists.txt
@@ -18,6 +18,7 @@ add_subdirectory(power)
 add_subdirectory(util)
 add_subdirectory(container)
 add_subdirectory(osal)
+add_subdirectory(pus)
 add_subdirectory(serialize)
 add_subdirectory(datapoollocal)
 add_subdirectory(storagemanager)
diff --git a/unittests/pus/CMakeLists.txt b/unittests/pus/CMakeLists.txt
new file mode 100644
index 00000000..ecd7fb49
--- /dev/null
+++ b/unittests/pus/CMakeLists.txt
@@ -0,0 +1,3 @@
+target_sources(${FSFW_TEST_TGT} PRIVATE
+    testService11.cpp
+)
diff --git a/unittests/pus/testService11.cpp b/unittests/pus/testService11.cpp
new file mode 100644
index 00000000..72708f09
--- /dev/null
+++ b/unittests/pus/testService11.cpp
@@ -0,0 +1,14 @@
+#include <fsfw/pus/Service11TelecommandScheduling.h>
+
+#include <catch2/catch_test_macros.hpp>
+
+#include "objects/systemObjectList.h"
+#include "tmtc/apid.h"
+#include "tmtc/pusIds.h"
+
+TEST_CASE("PUS Service 11", "[pus-srvc11]") {
+  Service11TelecommandScheduling<13> pusService11(objects::PUS_SERVICE_11_TC_SCHEDULER,
+                                                  apid::DEFAULT_APID, pus::PUS_SERVICE_11, nullptr);
+
+  // TODO test something...
+}
\ No newline at end of file