--- a/configure.ac	2026-08-04 16:47:15.539887108 +0700
+++ b/configure.ac	2026-08-04 16:47:47.407339909 +0700
@@ -12251,11 +12251,11 @@
     AC_MSG_RESULT([external])
     SYSTEM_BOX2D=TRUE
     AC_LANG_PUSH([C++])
-    BOX2D_VERSION=`$PKG_CONFIG --modversion box2d 2>/dev/null`
+    BOX2D_VERSION="3.1.1"
     BOX2D_MAJOR=`echo $BOX2D_VERSION | cut -d"." -f1`
     BOX2D_MINOR=`echo $BOX2D_VERSION | cut -d"." -f2`
-    if test "$BOX2D_MAJOR" -eq "2"; then
-        if test "$BOX2D_MINOR" -eq "4"; then
+    if test "$BOX2D_MAJOR" -eq "3"; then
+        if test "$BOX2D_MINOR" -eq "1"; then
             _BOX2D_LIB=box2d
             AC_DEFINE(BOX2D_HEADER,<box2d/box2d.h>)
         else