diff --git a/devel/tree-sitter-go-mod/Portfile b/devel/tree-sitter-go-mod/Portfile
index c48dbddda578..56b951ad012d 100644
--- a/devel/tree-sitter-go-mod/Portfile
+++ b/devel/tree-sitter-go-mod/Portfile
@@ -22,6 +22,9 @@ maintainers         {amake @amake} openmaintainer
 
 worksrcdir          ${worksrcdir}/src
 
+# parser.c: error: ‘for’ loop initial declaration used outside C99 mode
+configure.cflags-append -std=c99
+
 tree_sitter.libname gomod
 
 github.livecheck.branch main