--- src/_igraph/convert.c~	2023-10-12 12:24:54.000000000 -0500
+++ src/_igraph/convert.c	2023-10-24 11:13:19.320251800 -0500
@@ -23,6 +23,7 @@
 /************************ Conversion functions *************************/
 
 #include <limits.h>
+#include <ctype.h>
 #include "attributes.h"
 #include "convert.h"
 #include "edgeseqobject.h"