Index: sys/boot/i386/libi386/biosmem.c
===================================================================
--- sys/boot/i386/libi386/biosmem.c
+++ sys/boot/i386/libi386/biosmem.c
@@ -125,7 +125,7 @@
 		}
 
 		/*
-		 * Look for the largest segment in 'extended' memory beyond
+		 * Look for the highest segment in 'extended' memory beyond
 		 * 1MB but below 4GB.
 		 */
 		if ((smap.type == SMAP_TYPE_MEMORY) &&
@@ -140,9 +140,13 @@
 			if (smap.base + size > 0x100000000ull)
 				size = 0x100000000ull - smap.base;
 
-			if (size > high_heap_size) {
-				high_heap_size = size;
-				high_heap_base = smap.base;
+			/*
+			 * To make maximum space for the kernel and the modules,
+			 * set heap to use highest HEAP_MIN bytes below 4GB.
+			 */
+			if (high_heap_base < smap.base && size >= HEAP_MIN) {
+				high_heap_base = smap.base + size - HEAP_MIN;
+				high_heap_size = HEAP_MIN;
 			}
 		}
 	} while (v86.ebx != 0);
@@ -203,7 +207,11 @@
 	}
 
 	/* Set memtop to actual top of memory */
-	memtop = memtop_copyin = 0x100000 + bios_extmem;
+	if (high_heap_size != 0) {
+		memtop = memtop_copyin = high_heap_base;
+	} else {
+		memtop = memtop_copyin = 0x100000 + bios_extmem;
+	}
 
 	/*
 	 * If we have extended memory and did not find a suitable heap
@@ -213,6 +221,7 @@
 	if (bios_extmem >= HEAP_MIN && high_heap_size < HEAP_MIN) {
 		high_heap_size = HEAP_MIN;
 		high_heap_base = memtop - HEAP_MIN;
+		memtop = memtop_copyin = high_heap_base;
 	}
 }