diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 9c6357c03905..b64327722660 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -759,10 +759,12 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		break;
 	case ASHMEM_SET_SIZE:
 		ret = -EINVAL;
+		mutex_lock(&ashmem_mutex);
 		if (!asma->file) {
 			ret = 0;
 			asma->size = (size_t)arg;
 		}
+		mutex_unlock(&ashmem_mutex);
 		break;
 	case ASHMEM_GET_SIZE:
 		ret = asma->size;