diff --git a/hgdriver/hgdev/hg_scanner.cpp b/hgdriver/hgdev/hg_scanner.cpp
index dceeb01..be79da3 100644
--- a/hgdriver/hgdev/hg_scanner.cpp
+++ b/hgdriver/hgdev/hg_scanner.cpp
@@ -3978,7 +3978,7 @@ int hg_scanner::device_io_control(unsigned long code, void* data, unsigned* len)
 
 		memcpy(v, custom_gamma_val_, sizeof(*custom_gamma_val_));
 		if (len)
-			*len = image_prc_param_.bits.color_mode;
+			*len = sizeof(*custom_gamma_val_);
 
 		return SCANNER_ERR_OK;
 	}