diff --git a/src/client/util/util-avatar.vala b/src/client/util/util-avatar.vala
index d6c0ff6b..01075160 100644
--- a/src/client/util/util-avatar.vala
+++ b/src/client/util/util-avatar.vala
@@ -89,10 +89,12 @@ namespace Util.Avatar {
 
             // Get the first alphanumeric char of the last word of the string
             index = normalized.last_index_of_char(' ');
-            for (int i = 0; normalized.get_next_char(ref index, out c); i++) {
-                if (c.isalnum()) {
-                    buf.append_unichar(c);
-                    break;
+            if (index >= 0) {
+                for (int i = 0; normalized.get_next_char(ref index, out c); i++) {
+                    if (c.isalnum()) {
+                        buf.append_unichar(c);
+                        break;
+                    }
                 }
             }