diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9c2f59c8..4971f15f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 3.15)
 cmake_policy(SET CMP0091 NEW) # enable new "MSVC runtime library selection" (https://cmake.org/cmake/help/latest/variable/CMAKE_MSVC_RUNTIME_LIBRARY.html)
 
 project(libCZI 
-      VERSION 0.55.0
+      VERSION 0.55.1
       HOMEPAGE_URL "https://github.com/ZEISS/libczi"
       DESCRIPTION "libCZI is an Open Source Cross-Platform C++ library to read and write CZI")
 
diff --git a/Src/libCZI/Doc/version-history.markdown b/Src/libCZI/Doc/version-history.markdown
index 5996d5c5..0926eb83 100644
--- a/Src/libCZI/Doc/version-history.markdown
+++ b/Src/libCZI/Doc/version-history.markdown
@@ -9,4 +9,5 @@ version history                 {#version_history}
  0.54.0             | [71](https://github.com/ZEISS/libczi/pull/71)        | introduce 'streamsLib', add curl-based stream class
  0.54.2             | [74](https://github.com/ZEISS/libczi/pull/74)        | minor bug fix
  0.54.3             | [79](https://github.com/ZEISS/libczi/pull/79)        | add option _kCurlHttp_FollowLocation_ to follow HTTP redirects tp curl_http_inputstream
- 0.55.0             | [78](https://github.com/ZEISS/libczi/pull/78)        | optimization: for multi-tile-composition, check relevant tiles for visibility before loading them (and do not load/decode non-visible tiles)
\ No newline at end of file
+ 0.55.0             | [78](https://github.com/ZEISS/libczi/pull/78)        | optimization: for multi-tile-composition, check relevant tiles for visibility before loading them (and do not load/decode non-visible tiles)
+ 0.55.1             | [80](https://github.com/ZEISS/libczi/pull/80)        | bugfix for above optimization
\ No newline at end of file
diff --git a/Src/libCZI/SingleChannelAccessorBase.cpp b/Src/libCZI/SingleChannelAccessorBase.cpp
index b0a9c815..8a4e5a9f 100644
--- a/Src/libCZI/SingleChannelAccessorBase.cpp
+++ b/Src/libCZI/SingleChannelAccessorBase.cpp
@@ -119,7 +119,7 @@ std::vector<int> CSingleChannelAccessorBase::CheckForVisibility(const libCZI::In
         {                                                   //  some pixels which were not overdrawn by all the previous ones
             // this means - when drawing this subblock, some new pixels will be covered which were not covered before,
             //  so we need to draw this subblock, therefore we add it to our result vector
-            result.push_back(subblock_index);
+            result.push_back(i);
 
             covered_pixel_count = new_covered_pixel_count;
             if (new_covered_pixel_count == total_pixel_count)
diff --git a/Src/libCZI_UnitTests/test_TileAccessorCoverageOptimization.cpp b/Src/libCZI_UnitTests/test_TileAccessorCoverageOptimization.cpp
index 037020d9..e4e3d0a6 100644
--- a/Src/libCZI_UnitTests/test_TileAccessorCoverageOptimization.cpp
+++ b/Src/libCZI_UnitTests/test_TileAccessorCoverageOptimization.cpp
@@ -582,3 +582,29 @@ TEST(TileAccessorCoverageOptimization, CheckForVisibility_TestCase4)
     EXPECT_EQ(indices_of_visible_tiles[0], 1);
     EXPECT_EQ(indices_of_visible_tiles[1], 5);
 }
+
+TEST(TileAccessorCoverageOptimization, CheckForVisibility_TestCase5)
+{
+    static constexpr array<IntRect, 6> kSubBlocks{ IntRect{0,0,1,1}, IntRect{0,0,1,1}, IntRect{1,0,1,2}, IntRect{2,0,3,3}, IntRect{2,0,1,1}, IntRect{1,0,2,3} };
+
+    // the function CheckForVisibilityCore is supposed to return a vector with indices "as they are used to call into
+    // 'get_subblock_index'-functor" (**not** the subblock-index as returned from this functor). We check this here by
+    // returning a "non-zero-based"-index from the functor, where we then check that the returned vector contains the
+    // correct results according to above rule (and the function's documentation).
+
+    const auto indices_of_visible_tiles = CSingleChannelAccessorBaseToTestStub::CheckForVisibilityCore(
+        { 0, 0, 3, 3 },
+        kSubBlocks.size(),
+        [&](int index)->int
+        {
+            return index + 10;
+        },
+        [&](int subblock_index)->IntRect
+        {
+            return kSubBlocks[subblock_index - 10];
+        });
+
+    ASSERT_EQ(indices_of_visible_tiles.size(), 2);
+    EXPECT_EQ(indices_of_visible_tiles[0], 1);
+    EXPECT_EQ(indices_of_visible_tiles[1], 5);
+}