diff --git a/scripts/doc/append-xml-tags.py b/scripts/doc/append-xml-tags.py
index 4d8ff5284dda4c4b1829063d6e4a1ef5945f4e53..a6e6b4b27c65568c7cfbbc59159274e98460b65a 100755
--- a/scripts/doc/append-xml-tags.py
+++ b/scripts/doc/append-xml-tags.py
@@ -18,7 +18,7 @@ github_data_url = "https://github.com/ufz/ogs-data/tree/master"
 
 if len(sys.argv) != 4:
     print("Usage:")
-    print("{} EXT DATADIR DOCAUXDIR".format(sys.argv[0]))
+    print("{0} EXT DATADIR DOCAUXDIR".format(sys.argv[0]))
     sys.exit(1)
 
 ext       = sys.argv[1]
@@ -152,9 +152,9 @@ for (dirpath, _, filenames) in os.walk(docdir):
                             fh.write("- This is a required parameter.\n")
 
                         datatype = info[5]
-                        if datatype: fh.write("- Data type: <tt>{}</tt>\n".format(datatype))
+                        if datatype: fh.write("- Data type: <tt>{0}</tt>\n".format(datatype))
 
-                        fh.write("- Expanded tag path: {}\n".format(tagpath_expanded))
+                        fh.write("- Expanded tag path: {0}\n".format(tagpath_expanded))
 
                         fh.write("- Go to source code: [&rarr; ufz/ogs/master]({2}/{0}#L{1})\n"
                                 .format(path, line, github_src_url))
diff --git a/scripts/doc/normalize-param-cache.py b/scripts/doc/normalize-param-cache.py
index 942c5efe1fc0584740a408e35c0caef108c555e9..91a70b09baf7f24fde75ff92da76e1ae4c1d8218 100755
--- a/scripts/doc/normalize-param-cache.py
+++ b/scripts/doc/normalize-param-cache.py
@@ -51,7 +51,7 @@ for inline in sys.stdin:
 
         param_or_attr_comment = m.group(1)
         tag_path_comment = m.group(2).replace("__", ".")
-        debug(" {:>5}  //! {}".format(lineno, tag_path_comment))
+        debug(" {0:>5}  //! {1}".format(lineno, tag_path_comment))
         tag_name_comment = tag_path_comment.split(".")[-1]
 
         continue
@@ -83,7 +83,7 @@ for inline in sys.stdin:
         if state != "comment" or oldpath != path:
             write_out("NODOC", path, lineno, "NONE", param, paramtype, method)
         else:
-            debug(" {:>5}  {} {} ".format(lineno, param, paramtype))
+            debug(" {0:>5}  {1} {2} ".format(lineno, param, paramtype))
 
             if param != tag_name_comment:
                 debug("error: parameter name from comment and code do not match: "
@@ -91,7 +91,7 @@ for inline in sys.stdin:
                 write_out("NODOC", path, lineno, tag_path_comment, param, paramtype, method)
             elif lineno != oldlineno+1:
                 debug("error: the associated comment is not on the line preceding this one."
-                        + " line numbers {} vs. {}".format(oldlineno, lineno))
+                        + " line numbers {0} vs. {1}".format(oldlineno, lineno))
                 write_out("NODOC", path, lineno, tag_path_comment, param, paramtype, method)
             elif param_or_attr_comment == "param" and m.group(2) != "Param" and m.group(2) != "Subtree":
                 debug("error: comment says param but code says different.")
@@ -118,7 +118,7 @@ for inline in sys.stdin:
         else:
             if lineno != oldlineno+1:
                 debug("error: the associated comment is not on the line preceding this one."
-                        + " line numbers {} vs. {}".format(oldlineno, lineno))
+                        + " line numbers {0} vs. {1}".format(oldlineno, lineno))
                 write_out("NODOC", path, lineno, "UNKNOWN", "UNKNOWN", paramtype, method)
             elif param_or_attr_comment != "special":
                 debug("error: comment does not comment a special line.")