diff --git a/aegisub/configure.in b/aegisub/configure.in
index 752ac193d..0813d018a 100644
--- a/aegisub/configure.in
+++ b/aegisub/configure.in
@@ -489,7 +489,7 @@ int main(void) {
 } ])
 
   if test "$agi_cv_with_iconv_const" = "yes"; then
-    AC_DEFINE(ICONV_CONST, 1, [Enable if your version if iconv is const (annoying!)])
+    AC_DEFINE(AGI_ICONV_CONST, 1, [Enable if your version if iconv is const (annoying!)])
   fi
 fi