diff --git a/mfbt/IntegerPrintfMacros.h b/mfbt/IntegerPrintfMacros.h
index ff2415a86f91d..28bfc1436ed44 100644
--- a/mfbt/IntegerPrintfMacros.h
+++ b/mfbt/IntegerPrintfMacros.h
@@ -59,4 +59,9 @@
 #  define PRIXPTR "X"  /* uintptr_t */
 #endif
 
+/**
+ * For printing size_t.
+ */
+#define PRIuSIZE PRIuPTR
+
 #endif  /* mozilla_IntegerPrintfMacros_h_ */