diff --git a/tests/cts b/tests/cts
index c8e3003317..a79b5e9aa0 160000
--- a/tests/cts
+++ b/tests/cts
@@ -1 +1 @@
-Subproject commit c8e30033171b6c3bd69681796d8f2f6ae2d95322
+Subproject commit a79b5e9aa0142195e08dc4dfcb753429f1a5e50a
diff --git a/tools/imageio/exr.imageio/exrinput.cc b/tools/imageio/exr.imageio/exrinput.cc
index d1e149dc65..017b243422 100644
--- a/tools/imageio/exr.imageio/exrinput.cc
+++ b/tools/imageio/exr.imageio/exrinput.cc
@@ -258,6 +258,8 @@ void ExrInput::readImage(void* outputBuffer, size_t bufferByteCount,
                                   " images for each face and use those to create your KTX file.");
          }
     }
+    if (header.tiled && header.tile_level_mode != TINYEXR_TILE_ONE_LEVEL)
+        throw std::runtime_error(fmt::format("Multi-level tiled EXR images are not supported."));
     if ((header.tiled && image.tiles == nullptr) || (!header.tiled && image.images == nullptr))
         throw std::runtime_error(fmt::format("Invalid EXR file. {}",
             header.tiled ? "Tiled with no tiles" : "scanline with no images."));
@@ -297,11 +299,12 @@ void ExrInput::readImage(void* outputBuffer, size_t bufferByteCount,
         };
 
         for(int32_t tile = 0; tile < image.num_tiles; ++tile) {
-            for (int32_t ty = 0; ty < header.tile_size_y; ++ty) {
-                for (int32_t tx = 0; tx < header.tile_size_x; ++tx) {
+            for (int32_t ty = 0; ty < image.tiles[tile].height; ++ty) {
+                for (int32_t tx = 0; tx < image.tiles[tile].width; ++tx) {
                     auto x = image.tiles[tile].offset_x * header.tile_size_x + tx;
                     auto y = image.tiles[tile].offset_y * header.tile_size_y + ty;
                     auto* targetPixel = ptr + (y * width * numTargetChannels + x * numTargetChannels) * dataSize;
+                    assert(targetPixel < ptr + bufferByteCount && "outputBuffer overrun loading tiled .exr");
                     for (uint32_t c = 0; c < numTargetChannels; ++c) {
                         if (channels[c].has_value()) {
                             std::memcpy(targetPixel + c * dataSize, sourcePtr(*channels[c], tile, tx, ty), dataSize);
@@ -323,6 +326,7 @@ void ExrInput::readImage(void* outputBuffer, size_t bufferByteCount,
         for (uint32_t y = 0; y < height; ++y) {
             for (uint32_t x = 0; x < width; ++x) {
                 auto* targetPixel = ptr + (y * width * numTargetChannels + x * numTargetChannels) * dataSize;
+                assert(targetPixel < ptr + bufferByteCount && "outputBuffer overrun loading scanline .exr");
                 for (uint32_t c = 0; c < numTargetChannels; ++c) {
                     if (channels[c].has_value()) {
                         std::memcpy(targetPixel + c * dataSize, sourcePtr(*channels[c], x, y), dataSize);