diff --git a/src/libexpr/c/nix_api_external.h b/src/libexpr/c/nix_api_external.h
index daa74c5a8..c935bbe56 100644
--- a/src/libexpr/c/nix_api_external.h
+++ b/src/libexpr/c/nix_api_external.h
@@ -136,7 +136,7 @@ typedef struct NixCExternalValueDesc
      * or setting it to the empty string, will make the conversion throw an error.
      */
     void (*printValueAsJSON)(
-        void * self, EvalState *, int strict, nix_string_context * c, bool copyToStore, nix_string_return * res);
+        void * self, EvalState *, bool strict, nix_string_context * c, bool copyToStore, nix_string_return * res);
     /**
      * @brief Convert the external value to XML
      *