diff --git a/drivers/char/agp/agp.h b/drivers/char/agp/agp.h
index 35ab1a9f8e8..8955e7ff759 100644
--- a/drivers/char/agp/agp.h
+++ b/drivers/char/agp/agp.h
@@ -176,7 +176,7 @@ struct agp_bridge_data {
 #define I830_GMCH_MEM_MASK		0x1
 #define I830_GMCH_MEM_64M		0x1
 #define I830_GMCH_MEM_128M		0
-#define I830_GMCH_GMS_MASK		0xF0
+#define I830_GMCH_GMS_MASK		0x70
 #define I830_GMCH_GMS_DISABLED		0x00
 #define I830_GMCH_GMS_LOCAL		0x10
 #define I830_GMCH_GMS_STOLEN_512	0x20
@@ -190,6 +190,7 @@ struct agp_bridge_data {
 #define INTEL_I830_ERRSTS	0x92
 
 /* Intel 855GM/852GM registers */
+#define I855_GMCH_GMS_MASK		0xF0
 #define I855_GMCH_GMS_STOLEN_0M		0x0
 #define I855_GMCH_GMS_STOLEN_1M		(0x1 << 4)
 #define I855_GMCH_GMS_STOLEN_4M		(0x2 << 4)
diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index 7c69bf259ca..a5d0e95a227 100644
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -511,7 +511,7 @@ static void intel_i830_init_gtt_entries(void)
 		 */
 		if (IS_G33)
 			size = 0;
-		switch (gmch_ctrl & I830_GMCH_GMS_MASK) {
+		switch (gmch_ctrl & I855_GMCH_GMS_MASK) {
 		case I855_GMCH_GMS_STOLEN_1M:
 			gtt_entries = MB(1) - KB(size);
 			break;