diff -u -r ../notmuch-0.24.1/lib/message-property.cc ./lib/message-property.cc
--- ../notmuch-0.24.1/lib/message-property.cc	2017-04-01 14:29:38.000000000 +0200
+++ ./lib/message-property.cc	2017-04-07 00:48:00.914918764 +0200
@@ -51,7 +51,7 @@
     if (key == NULL || value == NULL)
 	return NOTMUCH_STATUS_NULL_POINTER;
 
-    if (index (key, '='))
+    if (strchr (key, '='))
 	return NOTMUCH_STATUS_ILLEGAL_ARGUMENT;
 
     term = talloc_asprintf (message, "%s=%s", key, value);