diff --git a/string_utils.cpp b/string_utils.cpp
index acf8588..13fdb9c 100644
--- a/string_utils.cpp
+++ b/string_utils.cpp
@@ -236,7 +236,6 @@
   va_end(ArgsCopy);
 }
 
-FORMAT(2, 3)
 void ScopedString::append(const char *Format, ...) {
   va_list Args;
   va_start(Args, Format);
@@ -244,7 +243,6 @@
   va_end(Args);
 }
 
-FORMAT(1, 2)
 void Printf(const char *Format, ...) {
   va_list Args;
   va_start(Args, Format);
diff --git a/string_utils.h b/string_utils.h
index 06d23d4..dd6ff78 100644
--- a/string_utils.h
+++ b/string_utils.h
@@ -26,15 +26,16 @@
     String.push_back('\0');
   }
   void append(const char *Format, va_list Args);
-  void append(const char *Format, ...);
+  void append(const char *Format, ...) FORMAT(2, 3);
   void output() const { outputRaw(String.data()); }
 
 private:
   Vector<char> String;
 };
 
-int formatString(char *Buffer, uptr BufferLength, const char *Format, ...);
-void Printf(const char *Format, ...);
+int formatString(char *Buffer, uptr BufferLength, const char *Format, ...)
+    FORMAT(3, 4);
+void Printf(const char *Format, ...) FORMAT(1, 2);
 
 } // namespace scudo