diff --git a/fs/gfs2/ops_inode.c b/fs/gfs2/ops_inode.c
index ae140c8..040b5a2 100644
--- a/fs/gfs2/ops_inode.c
+++ b/fs/gfs2/ops_inode.c
@@ -1425,6 +1425,10 @@
 	loff_t next = (offset + len - 1) >> sdp->sd_sb.sb_bsize_shift;
 	next = (next + 1) << sdp->sd_sb.sb_bsize_shift;
 
+	/* We only support the FALLOC_FL_KEEP_SIZE mode */
+	if (mode && (mode != FALLOC_FL_KEEP_SIZE))
+		return -EOPNOTSUPP;
+
 	offset = (offset >> sdp->sd_sb.sb_bsize_shift) <<
 		 sdp->sd_sb.sb_bsize_shift;