diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 9d2521a..9ddd6e9 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -45,7 +45,7 @@ static unsigned syscall_tell (int fd);
 static void syscall_close (int fd);
 
 static struct open_file *fd_get_file (int fd);
-static void validate_user_pointer (const void *ptr, size_t size);
+static void validate_user_pointer (const void *start, size_t size);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 typedef struct
@@ -397,16 +397,24 @@ fd_get_file (int fd)
   return hash_entry (e, struct open_file, elem);
 }
 
-/* Validates if a block of memory starting at PTR and of size SIZE bytes is
+/* Validates if a block of memory starting at START and of size SIZE bytes is
    fully contained within user virtual memory. Kills the thread (by calling
-   thread_exit) if the memory is invalid. Otherwise, returns the PTR given.
-   If the size is 0, the function does no checks and returns PTR.*/
+   thread_exit) if the memory is invalid. Otherwise, returns (nothing) normally.
+   If the size is 0, the function does no checks and returns the given ptr. */
 static void
-validate_user_pointer (const void *ptr, size_t size)
+validate_user_pointer (const void *start, size_t size)
 {
-  if (size > 0 && (ptr == NULL ||
-                   !is_user_vaddr (ptr) ||
-                   !is_user_vaddr (ptr + size - 1) ||
-                   pagedir_get_page (thread_current()->pagedir, ptr) == NULL))
+  if (size == 0)
+    return;
+
+  const void *end = start + size - 1;
+
+  if (start == NULL || !is_user_vaddr (start) || !is_user_vaddr (end))
     thread_exit ();
+
+  /* We now need to check if the entire memory block is mapped to physical
+     memory by the page table. */
+  for (const void *ptr = start; ptr <= end; ptr += PGSIZE)
+    if (pagedir_get_page (thread_current ()->pagedir, ptr) == NULL)
+      thread_exit ();
 }