diff --git a/README.md b/README.md
index e87ddfc..b1ea98a 100644
--- a/README.md
+++ b/README.md
@@ -4,9 +4,9 @@ A wiki engine.
 ## 0.9
 This is a development branch for 0.9 version. Features I want to implement in this release:
 * [x] Recent changes page.
-* [ ] Hypha deletion.
+* [x] Hypha deletion.
 * [ ] Hypha renaming.
-* [ ] Support async git ops.
+* [x] Support async git ops.
 
 ## Installation
 ```sh
diff --git a/history/history.go b/history/history.go
index cbd689b..c57ef96 100644
--- a/history/history.go
+++ b/history/history.go
@@ -99,10 +99,10 @@ func init() {
 }
 
 // I pronounce it as [gɪt͡ʃ].
+// gitsh is async-safe, therefore all other git-related functions in this module are too.
 func gitsh(args ...string) (out bytes.Buffer, err error) {
 	fmt.Printf("$ %v\n", args)
 	cmd := exec.Command(gitpath, args...)
-
 	cmd.Dir = util.WikiDir
 
 	b, err := cmd.CombinedOutput()
diff --git a/history/operations.go b/history/operations.go
index fecee81..149e795 100644
--- a/history/operations.go
+++ b/history/operations.go
@@ -4,10 +4,14 @@ package history
 
 import (
 	"fmt"
+	"sync"
 
 	"github.com/bouncepaw/mycorrhiza/util"
 )
 
+// gitMutex is used for blocking git operations to avoid clashes.
+var gitMutex = sync.Mutex{}
+
 // OpType is the type a history operation has. Callers shall set appropriate optypes when creating history operations.
 type OpType int
 
@@ -31,6 +35,7 @@ type HistoryOp struct {
 
 // Operation is a constructor of a history operation.
 func Operation(opType OpType) *HistoryOp {
+	gitMutex.Lock()
 	hop := &HistoryOp{
 		Errs:   []error{},
 		opType: opType,
@@ -75,6 +80,7 @@ func (hop *HistoryOp) Apply() *HistoryOp {
 		"--author='"+hop.name+" <"+hop.email+">'",
 		"--message="+hop.userMsg,
 	)
+	gitMutex.Unlock()
 	return hop
 }
 
diff --git a/metarrhiza b/metarrhiza
index ecaa76f..2c0e431 160000
--- a/metarrhiza
+++ b/metarrhiza
@@ -1 +1 @@
-Subproject commit ecaa76f841afcb3514b7061eb6708092bc17ee08
+Subproject commit 2c0e43199ed28f7022a38463a0eec3af3ecb03c9