diff --git a/pngrutil.c b/pngrutil.c
index 54b3771a7..16c628059 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -2540,7 +2540,7 @@ png_handle_iTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
       comp_type = *lang++;
    }
 
-   if (comp_flag != PNG_TEXT_COMPRESSION_zTXt)
+   if (comp_flag && comp_flag != PNG_TEXT_COMPRESSION_zTXt)
    {
       png_warning(png_ptr, "Unknown iTXt compression type");
       png_free(png_ptr, png_ptr->chunkdata);