diff --git a/ipc/sem.c b/ipc/sem.c
index db9d241..cc9ac35 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -584,10 +584,11 @@
 	return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
 }
 
-/** perform_atomic_semop - Perform (if possible) a semaphore operation
+/**
+ * perform_atomic_semop - Perform (if possible) a semaphore operation
  * @sma: semaphore array
  * @sops: array with operations that should be checked
- * @nsems: number of sops
+ * @nsops: number of operations
  * @un: undo array
  * @pid: pid that did the change
  *
@@ -595,7 +596,6 @@
  * Returns 1 if the operation is impossible, the caller must sleep.
  * Negative values are error codes.
  */
-
 static int perform_atomic_semop(struct sem_array *sma, struct sembuf *sops,
 			     int nsops, struct sem_undo *un, int pid)
 {
@@ -607,7 +607,7 @@
 		curr = sma->sem_base + sop->sem_num;
 		sem_op = sop->sem_op;
 		result = curr->semval;
-  
+
 		if (!sem_op && result)
 			goto would_block;
 
@@ -616,25 +616,24 @@
 			goto would_block;
 		if (result > SEMVMX)
 			goto out_of_range;
+
 		if (sop->sem_flg & SEM_UNDO) {
 			int undo = un->semadj[sop->sem_num] - sem_op;
-			/*
-	 		 *	Exceeding the undo range is an error.
-			 */
+			/* Exceeding the undo range is an error. */
 			if (undo < (-SEMAEM - 1) || undo > SEMAEM)
 				goto out_of_range;
+			un->semadj[sop->sem_num] = undo;
 		}
+
 		curr->semval = result;
 	}
 
 	sop--;
 	while (sop >= sops) {
 		sma->sem_base[sop->sem_num].sempid = pid;
-		if (sop->sem_flg & SEM_UNDO)
-			un->semadj[sop->sem_num] -= sop->sem_op;
 		sop--;
 	}
-	
+
 	return 0;
 
 out_of_range:
@@ -650,7 +649,10 @@
 undo:
 	sop--;
 	while (sop >= sops) {
-		sma->sem_base[sop->sem_num].semval -= sop->sem_op;
+		sem_op = sop->sem_op;
+		sma->sem_base[sop->sem_num].semval -= sem_op;
+		if (sop->sem_flg & SEM_UNDO)
+			un->semadj[sop->sem_num] += sem_op;
 		sop--;
 	}