diff --git a/headers/private/graphics/radeon_hd/radeon_hd.h b/headers/private/graphics/radeon_hd/radeon_hd.h
index 06cecceffd..bd290b7a07 100644
--- a/headers/private/graphics/radeon_hd/radeon_hd.h
+++ b/headers/private/graphics/radeon_hd/radeon_hd.h
@@ -76,6 +76,7 @@ struct radeon_shared_info {
 	uint8*			graphics_memory;
 	addr_t			physical_graphics_memory;
 	uint32			graphics_memory_size;
+	uint32			graphics_aperture_size;
 
 	bool			has_edid;
 	edid1_info		edid_info;
@@ -145,6 +146,9 @@ struct radeon_free_graphics_memory {
 	uint32	buffer_base;
 };
 
+// registers
+#define R6XX_CONFIG_APER_SIZE			0x5430	// r600>
+#define OLD_CONFIG_APER_SIZE			0x0108	// <r600
 
 // cursor
 #define RADEON_CURSOR_CONTROL			0x70080
diff --git a/src/add-ons/accelerants/radeon_hd/mode.cpp b/src/add-ons/accelerants/radeon_hd/mode.cpp
index ce8b9f34b6..968593296e 100644
--- a/src/add-ons/accelerants/radeon_hd/mode.cpp
+++ b/src/add-ons/accelerants/radeon_hd/mode.cpp
@@ -38,8 +38,6 @@ create_mode_list(void)
 	const color_space kRadeonHDSpaces[] = {B_RGB32_LITTLE, B_RGB24_LITTLE,
 		B_RGB16_LITTLE, B_RGB15_LITTLE, B_CMAP8};
 
-	// TODO : Read EDID for create_display_modes via AtomBios as well
-
 	gInfo->mode_list_area = create_display_modes("radeon HD modes",
 		gInfo->shared_info->has_edid ? &gInfo->shared_info->edid_info : NULL,
 		NULL, 0, kRadeonHDSpaces,
diff --git a/src/add-ons/kernel/drivers/graphics/radeon_hd/radeon_hd.cpp b/src/add-ons/kernel/drivers/graphics/radeon_hd/radeon_hd.cpp
index b5b5a1dae8..5e1cdbd3a8 100644
--- a/src/add-ons/kernel/drivers/graphics/radeon_hd/radeon_hd.cpp
+++ b/src/add-ons/kernel/drivers/graphics/radeon_hd/radeon_hd.cpp
@@ -109,19 +109,31 @@ radeon_hd_init(radeon_info &info)
 		info.shared_info->has_edid = false;
 	}
 
-	// Populate graphics_memory_size with graphics memory size in KB
+	// Populate graphics_memory/aperture_size with KB
 	if (info.shared_info->device_chipset >= RADEON_R800) {
 		// R800+ has memory stored in MB
 		info.shared_info->graphics_memory_size
 			= read32(info.registers + R6XX_CONFIG_MEMSIZE) << 10;
+		info.shared_info->graphics_aperture_size
+			= read32(info.registers + R6XX_CONFIG_APER_SIZE) << 10;
 	} else {
 		// R600-R700 has memory stored in bytes
 		info.shared_info->graphics_memory_size
 			= read32(info.registers + R6XX_CONFIG_MEMSIZE) >> 10;
+		info.shared_info->graphics_aperture_size
+			= read32(info.registers + R6XX_CONFIG_APER_SIZE) >> 10;
 	}
 
 	TRACE("card(%ld): found %ld MB memory on card.\n", info.id,
-		info.shared_info->graphics_memory_size / 1024);
+		info.shared_info->graphics_memory_size >> 10);
+	TRACE("card(%ld): found %ld MB aperture on card.\n", info.id,
+		info.shared_info->graphics_aperture_size >> 10);
+
+	// if there are more then 512MB memory on the card, only map
+	// the aperture size to prevent overflow of gart
+	if (info.shared_info->graphics_memory_size > 524288)
+		info.shared_info->graphics_memory_size
+			= info.shared_info->graphics_aperture_size;
 
 	TRACE("card(%ld): %s completed successfully!\n", info.id, __func__);
 	return B_OK;