diff --git a/dashboard_server.py b/dashboard_server.py
index cb67155..8ebb8cc 100644
--- a/dashboard_server.py
+++ b/dashboard_server.py
@@ -1920,9 +1920,10 @@ def handle_api_campaign_history(self, query_params: Dict[str, List[str]]):
         if "limit" in query_params:
             try:
                 limit = int(query_params["limit"][0])
-                limit = min(limit, _MAX_API_LIMIT)
             except (ValueError, IndexError):
-                limit = 25
+                self.send_error_response(400, "limit must be an integer")
+                return
+            limit = min(limit, _MAX_API_LIMIT)
         try:
             self.send_json_response(load_campaign_history(CAMPAIGN_HISTORY_ROOT, limit=limit))
         except Exception:
@@ -1934,9 +1935,10 @@ def handle_api_validation_history(self, query_params: Dict[str, List[str]]):
         if "limit" in query_params:
             try:
                 limit = int(query_params["limit"][0])
-                limit = min(limit, _MAX_API_LIMIT)
             except (ValueError, IndexError):
-                limit = 10
+                self.send_error_response(400, "limit must be an integer")
+                return
+            limit = min(limit, _MAX_API_LIMIT)
         try:
             self.send_json_response(load_validation_history(VALIDATION_HISTORY_ROOT, limit=limit))
         except Exception:
@@ -1948,9 +1950,10 @@ def handle_api_preflight_history(self, query_params: Dict[str, List[str]]):
         if "limit" in query_params:
             try:
                 limit = int(query_params["limit"][0])
-                limit = min(limit, _MAX_API_LIMIT)
             except (ValueError, IndexError):
-                limit = 10
+                self.send_error_response(400, "limit must be an integer")
+                return
+            limit = min(limit, _MAX_API_LIMIT)
         try:
             self.send_json_response(load_preflight_history(PREFLIGHT_HISTORY_ROOT, limit=limit))
         except Exception:
@@ -1969,9 +1972,10 @@ def handle_api_evidence_chain_history(self, query_params: Dict[str, List[str]]):
         if "limit" in query_params:
             try:
                 limit = int(query_params["limit"][0])
-                limit = min(limit, _MAX_API_LIMIT)
             except (ValueError, IndexError):
-                limit = 10
+                self.send_error_response(400, "limit must be an integer")
+                return
+            limit = min(limit, _MAX_API_LIMIT)
         try:
             self.send_json_response(load_evidence_chain_history(EVIDENCE_CHAIN_HISTORY_ROOT, limit=limit))
         except Exception:
diff --git a/test_dashboard_api_limits.py b/test_dashboard_api_limits.py
index 24239ae..2724c4d 100644
--- a/test_dashboard_api_limits.py
+++ b/test_dashboard_api_limits.py
@@ -99,6 +99,18 @@ def test_cleanup_non_integer_keep_latest_keeps_default(self):
             candidate_limit=25,
         )
 
+    def test_history_non_integer_limit_is_400(self):
+        handler = _handler()
+        for method in (
+            handler.handle_api_campaign_history,
+            handler.handle_api_validation_history,
+            handler.handle_api_preflight_history,
+            handler.handle_api_evidence_chain_history,
+        ):
+            handler.send_error_response.reset_mock()
+            method({"limit": ["nope"]})
+            handler.send_error_response.assert_called_once_with(400, "limit must be an integer")
+
     def test_options_preflight_does_not_require_a_bearer(self):
         old_token = dashboard_server.DASHBOARD_TOKEN
         old_origin = dashboard_server.DASHBOARD_CORS_ORIGIN