diff --git a/src/tinyexpr.cpp b/src/tinyexpr.cpp
index 4de6453f2..edff3c6c1 100644
--- a/src/tinyexpr.cpp
+++ b/src/tinyexpr.cpp
@@ -23,6 +23,7 @@
  */
 
 // This version has been altered and ported to C++ for inclusion in fish.
+#include "fallback.h"  // IWYU pragma: keep
 #include "tinyexpr.h"
 #include "wutil.h"