diff --git a/src/userfunc.c b/src/userfunc.c
index 5ef0f7d..33e73a9 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -14,6 +14,9 @@
 #include "vim.h"
 
 #if defined(FEAT_EVAL) || defined(PROTO)
+
+#define MAX_CALLBACK_DEPTH 20
+
 /*
  * All user-defined functions are found in this hashtable.
  */
@@ -3584,7 +3587,7 @@
     if (callback->cb_name == NULL || *callback->cb_name == NUL)
 	return FAIL;
 
-    if (callback_depth > p_mfd)
+    if (callback_depth > MAX_CALLBACK_DEPTH)
     {
 	emsg(_(e_command_too_recursive));
 	return FAIL;