Replace isgraph with our uppercase macro version
diff --git a/src/main.c b/src/main.c
index 4f9b3e4..d1b7009 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3422,7 +3422,7 @@
     }
     /* attempt to figure out if it is a string (since the tag numerical doesn't
        offer this info) and then output it as a string if so */
-    else if(pval && isgraph(ptr[0]) && isgraph(ptr[1]) && isgraph(ptr[2]))
+    else if(pval && ISGRAPH(ptr[0]) && ISGRAPH(ptr[1]) && ISGRAPH(ptr[2]))
       snprintf(value, sizeof(value), "\"%s\"", (char *)ptr);
     else if(pval) {
       snprintf(value, sizeof(value), "%p", pval);