diff --git a/indra/llimage/llpngwrapper.cpp b/indra/llimage/llpngwrapper.cpp
index c9d34f850..f515076c0 100644
--- a/indra/llimage/llpngwrapper.cpp
+++ b/indra/llimage/llpngwrapper.cpp
@@ -93,7 +93,7 @@ void LLPngWrapper::errorHandler(png_structp png_ptr, png_const_charp msg)
 void LLPngWrapper::readDataCallback(png_structp png_ptr, png_bytep dest, png_size_t length)
 {
 	PngDataInfo *dataInfo = (PngDataInfo *) png_get_io_ptr(png_ptr);
-	if (dataInfo->mOffset + length > dataInfo->mDataSize)
+	if (S32(dataInfo->mOffset + length) > dataInfo->mDataSize)
 	{
 		png_error(png_ptr, "Data read error. Requested data size exceeds available data size.");
 		return;