diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0d94c94..097b3a3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -136,6 +136,7 @@
 #define VM_EXEC		0x00000004
 #define VM_SHARED	0x00000008
 
+/* mprotect() hardcodes VM_MAYREAD >> 4 == VM_READ, and so for r/w/x bits. */
 #define VM_MAYREAD	0x00000010	/* limits for mprotect() etc */
 #define VM_MAYWRITE	0x00000020
 #define VM_MAYEXEC	0x00000040
diff --git a/mm/mprotect.c b/mm/mprotect.c
index e9fbd01..57577f6 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -248,7 +248,8 @@
 
 		newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 
-		if ((newflags & ~(newflags >> 4)) & 0xf) {
+		/* newflags >> 4 shift VM_MAY% in place of VM_% */
+		if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 			error = -EACCES;
 			goto out;
 		}