diff --git a/src/radeon_driver.c b/src/radeon_driver.c
index bf560f7..ed86b02 100644
--- a/src/radeon_driver.c
+++ b/src/radeon_driver.c
@@ -1396,6 +1396,9 @@ static void RADEONInitMemoryMap(ScrnInfoPtr pScrn)
 	aper_size = INREG(RADEON_CONFIG_APER_SIZE);
     }
 
+    if (aper_size > 0x10000000)
+	aper_size = 0x10000000;
+
     if (mem_size == 0)
 	mem_size = 0x800000;
 
@@ -1613,6 +1616,9 @@ static uint32_t RADEONGetAccessibleVRAM(ScrnInfoPtr pScrn)
     else
 	aper_size = INREG(RADEON_CONFIG_APER_SIZE) / 1024;
 
+    if (aper_size > 0x10000000)
+	aper_size = 0x10000000;
+
 #ifdef XF86DRI
     /* If we use the DRI, we need to check if it's a version that has the
      * bug of always cropping MC_FB_LOCATION to one aperture, in which case
@@ -1710,6 +1716,8 @@ static Bool RADEONPreInitVRAM(ScrnInfoPtr pScrn)
 
     /* Crop it to the size of the PCI BAR */
     bar_size = PCI_REGION_SIZE(info->PciInfo, 0) / 1024;
+    if (bar_size > 0x10000000)
+	bar_size = 0x10000000;
     if (bar_size == 0)
 	bar_size = 0x20000;
     if (accessible > bar_size)