diff --git a/include/utils/String8.h b/include/utils/String8.h
index b36f128..6abfb06 100644
--- a/include/utils/String8.h
+++ b/include/utils/String8.h
@@ -22,6 +22,7 @@
 #include <utils/Unicode.h>
 
 #include <string.h> // for strcmp
+#include <stdarg.h>
 
 // ---------------------------------------------------------------------------
 
@@ -70,6 +71,7 @@
 
             status_t            appendFormat(const char* fmt, ...)
                     __attribute__((format (printf, 2, 3)));
+            status_t            appendFormatV(const char* fmt, va_list args);
 
             // Note that this function takes O(N) time to calculate the value.
             // No cache value is stored.