diff --git a/dashboard/app/build/handler.go b/dashboard/app/build/handler.go
index 94504766..7834afa4 100644
--- a/dashboard/app/build/handler.go
+++ b/dashboard/app/build/handler.go
@@ -46,7 +46,13 @@ func commitHandler(r *http.Request) (interface{}, error) {
 	if r.Method == "GET" {
 		com.PackagePath = r.FormValue("packagePath")
 		com.Hash = r.FormValue("hash")
-		if err := datastore.Get(c, com.Key(c), com); err != nil {
+		err := datastore.Get(c, com.Key(c), com)
+		if com.Num == 0 && com.Desc == "" {
+			// Perf builder might have written an incomplete Commit.
+			// Pretend it doesn't exist, so that we can get complete details.
+			err = datastore.ErrNoSuchEntity
+		}
+		if err != nil {
 			if err == datastore.ErrNoSuchEntity {
 				// This error string is special.
 				// The commit watcher expects it.
diff --git a/dashboard/app/build/notify.go b/dashboard/app/build/notify.go
index bb12b21b..bbd710e7 100644
--- a/dashboard/app/build/notify.go
+++ b/dashboard/app/build/notify.go
@@ -15,6 +15,7 @@ import (
 	"net/http"
 	"net/url"
 	"regexp"
+	"runtime"
 	"sort"
 	"text/template"
 
@@ -216,6 +217,13 @@ func sendPerfFailMail(c appengine.Context, builder string, res *PerfResult) erro
 }
 
 func commonNotify(c appengine.Context, com *Commit, builder, logHash string) error {
+	if com.Num == 0 || com.Desc == "" {
+		stk := make([]byte, 10000)
+		n := runtime.Stack(stk, false)
+		stk = stk[:n]
+		c.Errorf("refusing to notify with com=%+v\n%s", *com, string(stk))
+		return fmt.Errorf("misuse of commonNotify")
+	}
 	if com.FailNotificationSent {
 		return nil
 	}