diff --git a/finbot/apps/cc/routes/challenges.py b/finbot/apps/cc/routes/challenges.py
index 2b44467b..3cd6034b 100644
--- a/finbot/apps/cc/routes/challenges.py
+++ b/finbot/apps/cc/routes/challenges.py
@@ -37,7 +37,11 @@ def _challenge_list_with_stats(db) -> list[dict]:
         total_attempts = sum(p.attempts for p in progress_rows)
         hints_used = sum(p.hints_used for p in progress_rows)
 
-        completed_rows = [p for p in progress_rows if p.status == "completed" and p.completion_time_seconds]
+        completed_rows = [
+            p
+            for p in progress_rows
+            if p.status == "completed" and p.completion_time_seconds is not None
+        ]
         avg_solve = (
             int(sum(p.completion_time_seconds for p in completed_rows) / len(completed_rows))
             if completed_rows else None
diff --git a/finbot/apps/cc/templates/pages/challenges.html b/finbot/apps/cc/templates/pages/challenges.html
index 60a819cb..5d4f595f 100644
--- a/finbot/apps/cc/templates/pages/challenges.html
+++ b/finbot/apps/cc/templates/pages/challenges.html
@@ -100,7 +100,7 @@
                             {% endif %}
                         </td>
                         <td class="px-3 py-3 text-right tabular-nums text-text-2">
-                            {% if c.avg_solve_seconds %}
+                            {% if c.avg_solve_seconds is not none %}
                             {{ (c.avg_solve_seconds // 60) }}m
                             {% else %}
                             <span class="text-text-3">-</span>
diff --git a/tests/unit/apps/cc/test_challenges.py b/tests/unit/apps/cc/test_challenges.py
new file mode 100644
index 00000000..08ed30e9
--- /dev/null
+++ b/tests/unit/apps/cc/test_challenges.py
@@ -0,0 +1,83 @@
+import re
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+from jinja2 import Environment, FileSystemLoader
+
+from finbot.apps.cc.routes.challenges import _challenge_list_with_stats
+
+
+def _challenge_stats(*completion_times: int | None) -> dict:
+    challenge = SimpleNamespace(
+        category="test",
+        description="",
+        detector_class="MissingDetector",
+        difficulty="beginner",
+        hints=None,
+        id="test-challenge",
+        is_active=True,
+        labels=None,
+        points=100,
+        prerequisites=None,
+        subcategory=None,
+        title="Test Challenge",
+    )
+    progress_rows = [
+        SimpleNamespace(
+            attempts=1,
+            completion_time_seconds=completion_time,
+            hints_used=0,
+            status="completed",
+            user_id=f"user-{index}",
+        )
+        for index, completion_time in enumerate(completion_times)
+    ]
+    challenge_query = MagicMock()
+    challenge_query.order_by.return_value.all.return_value = [challenge]
+    progress_query = MagicMock()
+    progress_query.filter.return_value.all.return_value = progress_rows
+    db = MagicMock()
+    db.query.side_effect = [challenge_query, progress_query]
+
+    return _challenge_list_with_stats(db)[0]
+
+
+def test_average_solve_time_includes_zero_and_excludes_missing_values() -> None:
+    stats = _challenge_stats(0, 10, None)
+
+    assert stats["completions"] == 3
+    assert stats["avg_solve_seconds"] == 5
+
+
+def test_zero_second_average_is_preserved() -> None:
+    stats = _challenge_stats(0)
+
+    assert stats["avg_solve_seconds"] == 0
+
+
+def test_challenge_template_renders_zero_second_average() -> None:
+    template_dir = Path(__file__).parents[4] / "finbot" / "apps" / "cc" / "templates"
+    template = Environment(loader=FileSystemLoader(template_dir)).get_template(
+        "pages/challenges.html"
+    )
+    stats = _challenge_stats(0)
+
+    rendered = template.render(
+        categories=["test"],
+        challenges=[stats],
+        coverage=[],
+        difficulties=["beginner"],
+        summary={
+            "active": 1,
+            "inactive": 0,
+            "invalid_detectors": 1,
+            "solved": 1,
+            "total": 1,
+            "unsolved": 0,
+        },
+        url_for=lambda *args, **kwargs: "/static",
+        user=None,
+    )
+
+    assert re.search(r">\s*0m\s*<", rendered)