diff --git a/src/sinol_make/__init__.py b/src/sinol_make/__init__.py
index ade9cd03..af2a9cc0 100644
--- a/src/sinol_make/__init__.py
+++ b/src/sinol_make/__init__.py
@@ -9,7 +9,7 @@
 from sinol_make import util, oiejq
 
 
-__version__ = "1.5.20"
+__version__ = "1.5.21"
 
 
 def configure_parsers():
diff --git a/src/sinol_make/commands/inwer/__init__.py b/src/sinol_make/commands/inwer/__init__.py
index 7909f620..e0755876 100644
--- a/src/sinol_make/commands/inwer/__init__.py
+++ b/src/sinol_make/commands/inwer/__init__.py
@@ -143,6 +143,10 @@ def get_id(test, func=str.isalpha):
             last_test = test
 
         def is_next(last, curr):
+            if last == "" and curr != "a":
+                return False
+            elif last == "":
+                return True
             i = len(last) - 1
             while i >= 0:
                 if last[i] != 'z':
diff --git a/tests/commands/inwer/test_unit.py b/tests/commands/inwer/test_unit.py
index 53bb3787..0cb7818d 100644
--- a/tests/commands/inwer/test_unit.py
+++ b/tests/commands/inwer/test_unit.py
@@ -103,3 +103,11 @@ def test_verify_tests_order():
     command.tests.append("abc11ocen.in")
 
     command.verify_tests_order()
+
+    command.tests = ["abc0.in", "abc0a.in", "abc0b.in",
+                     "abc1.in", "abc1a.in", "abc1b.in"]
+    command.verify_tests_order()
+
+    command.tests.remove("abc0a.in")
+    with pytest.raises(SystemExit):
+        command.verify_tests_order()