diff --git a/mm/mmap.c b/mm/mmap.c
index da3fa90..4043194 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -143,7 +143,11 @@
 	   leave 3% of the size of this process for other processes */
 	allowed -= current->mm->total_vm / 32;
 
-	if (atomic_read(&vm_committed_space) < allowed)
+	/*
+	 * cast `allowed' as a signed long because vm_committed_space
+	 * sometimes has a negative value
+	 */
+	if (atomic_read(&vm_committed_space) < (long)allowed)
 		return 0;
 
 	vm_unacct_memory(pages);