diff --git a/src/calls-call.c b/src/calls-call.c
index e1d3d6e..3db3299 100644
--- a/src/calls-call.c
+++ b/src/calls-call.c
@@ -38,7 +38,14 @@ calls_call_state_to_string (GString        *string,
   GEnumValue *value;
 
   klass = g_type_class_ref (CALLS_TYPE_CALL_STATE);
+
   value = g_enum_get_value (klass, (gint)state);
+  if (!value)
+    {
+      return g_string_printf (string,
+                              "Unknown call state (%d)",
+                              (gint)state);
+    }
 
   g_string_assign (string, value->value_nick);
   string->str[0] = g_ascii_toupper (string->str[0]);