diff --git a/app/pdb/image-cmds.c b/app/pdb/image-cmds.c
index 5086deaff8..42c9b6c591 100644
--- a/app/pdb/image-cmds.c
+++ b/app/pdb/image-cmds.c
@@ -2263,7 +2263,35 @@ image_set_file_invoker (GimpProcedure         *procedure,
 
   if (success)
     {
-      gimp_image_set_file (image, file);
+      gchar *uri;
+      gchar *folded_uri;
+      gchar *folded_ext;
+
+      uri        = g_file_get_uri (file);
+      folded_uri = g_utf8_casefold (uri, -1);
+      folded_ext = g_utf8_casefold (".xcf", -1);
+
+      if (! g_str_has_suffix (folded_uri, folded_ext))
+        {
+          gchar *dot = g_strrstr (uri, ".");
+
+          if (dot != NULL && strstr (dot + 1, G_DIR_SEPARATOR_S) == NULL)
+            g_printerr ("%s: failure to set file '%s' with extension '%s'. "
+                        "The extension must be '.xcf'.\n",
+                        "gimp_image_set_file", uri, dot + 1);
+          else
+            g_printerr ("%s: failure to set file '%s' without extension. "
+                        "The extension must be '.xcf'.\n",
+                        "gimp_image_set_file", uri);
+
+          success = FALSE;
+        }
+      if (success)
+        gimp_image_set_file (image, file);
+
+      g_free (uri);
+      g_free (folded_uri);
+      g_free (folded_ext);
     }
 
   return gimp_procedure_get_return_values (procedure, success,
@@ -4968,8 +4996,9 @@ register_image_procs (GimpPDB *pdb)
   gimp_object_set_static_name (GIMP_OBJECT (procedure),
                                "gimp-image-set-file");
   gimp_procedure_set_static_help (procedure,
-                                  "Sets the specified image's file.",
-                                  "This procedure sets the specified image's file.",
+                                  "Sets the specified XCF image's file.",
+                                  "This procedure sets the specified image's file.\n"
+                                  "This is to set the XCF file associated with your image. In particular, do not use this function to set the imported file in file import plug-ins. This is done by the core process.",
                                   NULL);
   gimp_procedure_set_static_attribution (procedure,
                                          "Spencer Kimball & Peter Mattis",
diff --git a/libgimp/gimpimage_pdb.c b/libgimp/gimpimage_pdb.c
index 4a3d9d19ec..9c59564c52 100644
--- a/libgimp/gimpimage_pdb.c
+++ b/libgimp/gimpimage_pdb.c
@@ -2615,9 +2615,12 @@ gimp_image_get_file (GimpImage *image)
  * @image: The image.
  * @file: The new image file.
  *
- * Sets the specified image's file.
+ * Sets the specified XCF image's file.
  *
  * This procedure sets the specified image's file.
+ * This is to set the XCF file associated with your image. In
+ * particular, do not use this function to set the imported file in
+ * file import plug-ins. This is done by the core process.
  *
  * Returns: TRUE on success.
  **/
diff --git a/pdb/groups/image.pdb b/pdb/groups/image.pdb
index 26abaa43f6..8d228b4ab3 100644
--- a/pdb/groups/image.pdb
+++ b/pdb/groups/image.pdb
@@ -2322,10 +2322,14 @@ CODE
 }
 
 sub image_set_file {
-    $blurb = "Sets the specified image's file.";
+    $blurb = "Sets the specified XCF image's file.";
 
     $help = <<'HELP';
 This procedure sets the specified image's file.
+
+This is to set the XCF file associated with your image. In particular, do not
+use this function to set the imported file in file import plug-ins. This is done
+by the core process.
 HELP
 
     &std_pdb_misc;
@@ -2340,7 +2344,35 @@ HELP
     %invoke = (
         code => <<'CODE'
 {
-  gimp_image_set_file (image, file);
+  gchar *uri;
+  gchar *folded_uri;
+  gchar *folded_ext;
+
+  uri        = g_file_get_uri (file);
+  folded_uri = g_utf8_casefold (uri, -1);
+  folded_ext = g_utf8_casefold (".xcf", -1);
+
+  if (! g_str_has_suffix (folded_uri, folded_ext))
+    {
+      gchar *dot = g_strrstr (uri, ".");
+
+      if (dot != NULL && strstr (dot + 1, G_DIR_SEPARATOR_S) == NULL)
+        g_printerr ("%s: failure to set file '%s' with extension '%s'. "
+                    "The extension must be '.xcf'.\n",
+                    "gimp_image_set_file", uri, dot + 1);
+      else
+        g_printerr ("%s: failure to set file '%s' without extension. "
+                    "The extension must be '.xcf'.\n",
+                    "gimp_image_set_file", uri);
+
+      success = FALSE;
+    }
+  if (success)
+    gimp_image_set_file (image, file);
+
+  g_free (uri);
+  g_free (folded_uri);
+  g_free (folded_ext);
 }
 CODE
     );