diff --git a/include/utils/String8.h b/include/utils/String8.h
index 4e41410f4..ef0b51a44 100644
--- a/include/utils/String8.h
+++ b/include/utils/String8.h
@@ -171,7 +171,8 @@ public:
             status_t            append(const char* other);
             status_t            append(const char* other, size_t numChars);
 
-            status_t            appendFormat(const char* fmt, ...);
+            status_t            appendFormat(const char* fmt, ...)
+                    __attribute__((format (printf, 2, 3)));
 
             // Note that this function takes O(N) time to calculate the value.
             // No cache value is stored.