diff --git a/preproc/preproc/preprocessor.py b/preproc/preproc/preprocessor.py
index 016439c810ed16dc92f7c241b22fe5cad3114de5..b79088c65b954697cf80336b06137822335f48df 100644
--- a/preproc/preproc/preprocessor.py
+++ b/preproc/preproc/preprocessor.py
@@ -21,8 +21,8 @@ class PreProcessor:
         self.dst_file = dst_file
         self.imported_strs = []
         self._already_imported_classes = {}  # name -> full_name
-        self._import_regexp = re.compile("import [A-Za-z.]+;")
-        self._imported_class_regexp = re.compile("[A-Za-z.]+;")
+        self._import_regexp = re.compile("import [A-Za-z.0-9]+;")
+        self._imported_class_regexp = re.compile("[A-Za-z.0-9]+;")
         self._imported_classes = defaultdict(lambda: [])  # name -> embedding files
         if not os.path.isfile(src_file):
             raise PreProcessorError("Source file '{}' isn't a file".format(src_file))
@@ -127,7 +127,7 @@ def is_importable_file(file: str) -> bool:
             if line.startswith("package "):
                 has_package = True
             elif line.startswith("public class "):
-                match = re.search("[A-Za-z_]+", line.replace("public class ", ""))
+                match = re.search("[A-Za-z_0-9]+", line.replace("public class ", ""))
                 if match:
                     has_public_class = True
                     if match.group(0) != name: