diff --git a/mwparserfromhell/nodes/template.py b/mwparserfromhell/nodes/template.py
index 29a2a16..7240051 100644
--- a/mwparserfromhell/nodes/template.py
+++ b/mwparserfromhell/nodes/template.py
@@ -76,7 +76,7 @@ class Template(Node):
                 code.replace(node, node.replace(char, replacement))
 
     def _blank_param_value(self, value):
-        match = re.search("^(\s*).*?(\s*)$", unicode(value), FLAGS)
+        match = re.search(r"^(\s*).*?(\s*)$", unicode(value), FLAGS)
         value.nodes = [Text(match.group(1)), Text(match.group(2))]
 
     def _select_theory(self, theories):
@@ -149,10 +149,8 @@ class Template(Node):
             else:
                 int_keys = set()
                 for param in self.params:
-                    try:
+                    if re.match(r"[1-9][0-9]*$", param.name.strip()):
                         int_keys.add(int(unicode(param.name)))
-                    except ValueError:
-                        pass
                 expected = min(set(range(1, len(int_keys) + 2)) - int_keys)
                 if expected == int_name:
                     showkey = False
diff --git a/mwparserfromhell/parser/builder.py b/mwparserfromhell/parser/builder.py
index c4a0055..9d046a6 100644
--- a/mwparserfromhell/parser/builder.py
+++ b/mwparserfromhell/parser/builder.py
@@ -20,6 +20,8 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
+import re
+
 from . import tokens
 from ..nodes import Heading, HTMLEntity, Tag, Template, Text
 from ..nodes.extras import Attribute, Parameter
@@ -76,11 +78,12 @@ class Builder(object):
                     name = self._pop()
                 default = self._wrap(unicode(min(int_key_range - int_keys)))
                 param = self._handle_parameter(default)
-                try:
+                if re.match(r"[1-9][0-9]*$", param.name.strip()):
+                    # We try a more restrictive test for integers than
+                    # try: int(), because "01" as a key will pass through int()
+                    # correctly but is not a valid integer key in wikicode:
                     int_keys.add(int(unicode(param.name)))
                     int_key_range.add(len(int_keys) + 1)
-                except ValueError:
-                    pass
                 params.append(param)
             elif isinstance(token, tokens.TemplateClose):
                 if not params: