diff --git a/include/utils/String8.h b/include/utils/String8.h
index c4b18a4ca..0b18fe3d2 100644
--- a/include/utils/String8.h
+++ b/include/utils/String8.h
@@ -171,6 +171,8 @@ public:
             status_t            append(const char* other);
             status_t            append(const char* other, size_t numChars);
 
+            status_t            appendFormat(const char* fmt, ...);
+
             // Note that this function takes O(N) time to calculate the value.
             // No cache value is stored.
             size_t              getUtf32Length() const;
diff --git a/libs/utils/String8.cpp b/libs/utils/String8.cpp
index 82776f47a..1c4f80c1f 100644
--- a/libs/utils/String8.cpp
+++ b/libs/utils/String8.cpp
@@ -372,6 +372,27 @@ status_t String8::append(const char* other, size_t otherLen)
     return real_append(other, otherLen);
 }
 
+status_t String8::appendFormat(const char* fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+
+    int result = NO_ERROR;
+    int n = vsnprintf(NULL, 0, fmt, ap);
+    if (n != 0) {
+        size_t oldLength = length();
+        char* buf = lockBuffer(oldLength + n);
+        if (buf) {
+            vsnprintf(buf + oldLength, n + 1, fmt, ap);
+        } else {
+            result = NO_MEMORY;
+        }
+    }
+
+    va_end(ap);
+    return result;
+}
+
 status_t String8::real_append(const char* other, size_t otherLen)
 {
     const size_t myLen = bytes();
@@ -411,15 +432,16 @@ status_t String8::unlockBuffer(size_t size)
     if (size != this->size()) {
         SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
             ->editResize(size+1);
-        if (buf) {
-            char* str = (char*)buf->data();
-            str[size] = 0;
-            mString = str;
-            return NO_ERROR;
+        if (! buf) {
+            return NO_MEMORY;
         }
+
+        char* str = (char*)buf->data();
+        str[size] = 0;
+        mString = str;
     }
-    
-    return NO_MEMORY;
+
+    return NO_ERROR;
 }
 
 ssize_t String8::find(const char* other, size_t start) const