diff --git a/src/typval.c b/src/typval.c
index 3a0e2e5..c859122 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -471,6 +471,23 @@
 }
 
 /*
+ * Give an error and return FAIL unless "args[idx]" is a blob.
+ */
+    int
+check_for_blob_arg(typval_T *args, int idx)
+{
+    if (args[idx].v_type != VAR_BLOB)
+    {
+	if (idx >= 0)
+	    semsg(_(e_blob_required_for_argument_nr), idx + 1);
+	else
+	    emsg(_(e_blob_required));
+	return FAIL;
+    }
+    return OK;
+}
+
+/*
  * Give an error and return FAIL unless "args[idx]" is a list.
  */
     int