diff --git a/plug-ins/script-fu/libscriptfu/script-fu-run-func.c b/plug-ins/script-fu/libscriptfu/script-fu-run-func.c
index 4a2eea3361..8da79c2ce9 100644
--- a/plug-ins/script-fu/libscriptfu/script-fu-run-func.c
+++ b/plug-ins/script-fu/libscriptfu/script-fu-run-func.c
@@ -175,11 +175,8 @@ script_fu_run_procedure (GimpProcedure       *procedure,
       }
 
     case GIMP_RUN_NONINTERACTIVE:
-      /* Verify actual args count equals declared arg count.
-       * Scripts declare args except run_mode (SF hides it.)
-       * pspecs have run_mode and one extra internal pspec, thus +2.
-       */
-      if (n_pspecs != script->n_args + n_aux_args + 2)
+      /* Verify actual args count equals declared arg count. */
+      if (n_pspecs != script->n_args + n_aux_args + SF_ARG_TO_CONFIG_OFFSET)
         status = GIMP_PDB_CALLING_ERROR;
 
       if (status == GIMP_PDB_SUCCESS)
diff --git a/plug-ins/script-fu/libscriptfu/script-fu-script.c b/plug-ins/script-fu/libscriptfu/script-fu-script.c
index 10d67b06cb..62a1e4aa3c 100644
--- a/plug-ins/script-fu/libscriptfu/script-fu-script.c
+++ b/plug-ins/script-fu/libscriptfu/script-fu-script.c
@@ -357,7 +357,7 @@ script_fu_script_get_command_from_params (SFScript             *script,
   for (i = 0; i < script->n_args; i++)
     {
       GValue      value = G_VALUE_INIT;
-      GParamSpec *pspec = pspecs[i + 1];
+      GParamSpec *pspec = pspecs[i + SF_ARG_TO_CONFIG_OFFSET];
 
       g_value_init (&value, pspec->value_type);
       g_object_get_property (G_OBJECT (config), pspec->name, &value);
@@ -495,10 +495,10 @@ script_fu_script_param_init (SFScript             *script,
   if (script->n_args > n &&
       arg->type == type  &&
       /* The first pspec is "procedure", the second is "run-mode". */
-      n_pspecs > n + 2)
+      n_pspecs > n + SF_ARG_TO_CONFIG_OFFSET)
     {
       GValue      value = G_VALUE_INIT;
-      GParamSpec *pspec = pspecs[n + 2];
+      GParamSpec *pspec = pspecs[n + SF_ARG_TO_CONFIG_OFFSET];
 
       g_value_init (&value, pspec->value_type);
       g_object_get_property (G_OBJECT (config), pspec->name, &value);
diff --git a/plug-ins/script-fu/libscriptfu/script-fu-types.h b/plug-ins/script-fu/libscriptfu/script-fu-types.h
index 91646cf359..7603738c70 100644
--- a/plug-ins/script-fu/libscriptfu/script-fu-types.h
+++ b/plug-ins/script-fu/libscriptfu/script-fu-types.h
@@ -94,6 +94,14 @@ typedef struct
   GType           proc_class; /* GimpProcedure or GimpImageProcedure. */
 } SFScript;
 
+/* ScriptFu keeps array of SFArg, it's private arg specs.
+ * Scripts declare args except run_mode (SF hides it.)
+ * A GimpConfig has two extra leading properties, for procedure and run_mode.
+ * A set of GParamSpecs is derived from a config and also has two extra.
+ * This defines the difference in length between SF's arg spec array and a config.
+ */
+#define SF_ARG_TO_CONFIG_OFFSET 2
+
 typedef struct
 {
   SFScript *script;   /* script which defined this menu path and label */