diff --git a/lib/message-property.cc b/lib/message-property.cc
index 0b13cac3..f32d5550 100644
--- a/lib/message-property.cc
+++ b/lib/message-property.cc
@@ -51,7 +51,7 @@ _notmuch_message_modify_property (notmuch_message_t *message, const char *key, c
     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);
diff --git a/lib/message.cc b/lib/message.cc
index f8215a49..c2721191 100644
--- a/lib/message.cc
+++ b/lib/message.cc
@@ -1843,7 +1843,7 @@ _notmuch_message_ensure_property_map (notmuch_message_t *message)
 	const char *key;
 	char *value;
 
-	value = index(node->string, '=');
+	value = strchr(node->string, '=');
 	if (!value)
 	    INTERNAL_ERROR ("malformed property term");