diff --git a/IO/src/ImageLoaderKTX.cpp b/IO/src/ImageLoaderKTX.cpp
index 60d4ec1..50f3511 100644
--- a/IO/src/ImageLoaderKTX.cpp
+++ b/IO/src/ImageLoaderKTX.cpp
@@ -75,7 +75,7 @@ class ByteReader {
   { }
 
   bool Advance(uint32 nBytes) {
-    if(nBytes < m_BytesLeft) {
+    if(nBytes > m_BytesLeft) {
       assert(!"Cannot read any more, unexpected bytes!");
       return false;
     }
@@ -278,6 +278,7 @@ bool ImageLoaderKTX::ReadData() {
     switch(glInternalFormat) {
       case GL_COMPRESSED_RGBA_BPTC_UNORM:
         m_Format = FasTC::eCompressionFormat_BPTC;
+        break;
       default:
         fprintf(stderr, "KTX loader - texture format (0x%x) unsupported!\n", glInternalFormat);
         return false;
diff --git a/IO/src/ImageWriterKTX.cpp b/IO/src/ImageWriterKTX.cpp
index 20712f5..e9aa7e1 100644
--- a/IO/src/ImageWriterKTX.cpp
+++ b/IO/src/ImageWriterKTX.cpp
@@ -123,7 +123,7 @@ bool ImageWriterKTX::WriteImage() {
   if(ci) {
     wtr.Write(0);  // glType
     wtr.Write(1);  // glTypeSize
-    wtr.Write(GL_RGBA);  // glFormat
+    wtr.Write(0);  // glFormat must be zero for compressed images...
     switch(ci->GetFormat()) {
     case FasTC::eCompressionFormat_BPTC:
       wtr.Write(GL_COMPRESSED_RGBA_BPTC_UNORM);  // glInternalFormat