diff --git a/injectproxy/routes.go b/injectproxy/routes.go
index 61a2a89b..fb673d05 100644
--- a/injectproxy/routes.go
+++ b/injectproxy/routes.go
@@ -389,8 +389,8 @@ func NewRoutes(upstream *url.URL, label string, extractLabeler ExtractLabeler, o
 
 	r.mux = mux
 	r.modifiers = map[string]func(*http.Response) error{
-		"/api/v1/rules":  modifyAPIResponse(r.filterRules),
-		"/api/v1/alerts": modifyAPIResponse(r.filterAlerts),
+		upstream.Path + "/api/v1/rules":  modifyAPIResponse(r.filterRules),
+		upstream.Path + "/api/v1/alerts": modifyAPIResponse(r.filterAlerts),
 	}
 	proxy.ModifyResponse = r.ModifyResponse
 	proxy.ErrorHandler = r.errorHandler
diff --git a/injectproxy/rules_test.go b/injectproxy/rules_test.go
index 8c56b607..6702a3fc 100644
--- a/injectproxy/rules_test.go
+++ b/injectproxy/rules_test.go
@@ -439,10 +439,11 @@ func validAlerts() http.Handler {
 
 func TestRules(t *testing.T) {
 	for _, tc := range []struct {
-		labelv     []string
-		upstream   http.Handler
-		reqHeaders http.Header
-		opts       []Option
+		labelv             []string
+		upstream           http.Handler
+		upstreamPathPrefix string
+		reqHeaders         http.Header
+		opts               []Option
 
 		expCode int
 		golden  string
@@ -557,10 +558,23 @@ func TestRules(t *testing.T) {
 			expCode: http.StatusOK,
 			golden:  "rules_with_active_alerts.golden",
 		},
+		{
+			labelv:             []string{"ns1"},
+			upstream:           validRules(),
+			upstreamPathPrefix: "/prometheus",
+
+			expCode: http.StatusOK,
+			golden:  "rules_match_namespace_ns1_non_root_upstream.golden",
+		},
 	} {
 		t.Run(fmt.Sprintf("%s=%s", proxyLabel, tc.labelv), func(t *testing.T) {
 			m := newMockUpstream(tc.upstream)
 			defer m.Close()
+
+			if tc.upstreamPathPrefix != "" {
+				m.url.Path = tc.upstreamPathPrefix + m.url.Path
+			}
+
 			r, err := NewRoutes(
 				m.url,
 				proxyLabel,
diff --git a/injectproxy/testdata/rules_match_namespace_ns1_non_root_upstream.golden b/injectproxy/testdata/rules_match_namespace_ns1_non_root_upstream.golden
new file mode 100644
index 00000000..cbb43610
--- /dev/null
+++ b/injectproxy/testdata/rules_match_namespace_ns1_non_root_upstream.golden
@@ -0,0 +1,127 @@
+{
+  "status": "success",
+  "data": {
+    "groups": [
+      {
+        "name": "group1",
+        "file": "testdata/rules1.yml",
+        "rules": [
+          {
+            "name": "metric1",
+            "query": "0",
+            "labels": {
+              "namespace": "ns1"
+            },
+            "health": "ok",
+            "evaluationTime": 0.000214303,
+            "lastEvaluation": "2024-04-29T14:23:52.403557247+02:00",
+            "type": "recording"
+          },
+          {
+            "name": "metric2",
+            "query": "1",
+            "labels": {
+              "namespace": "ns1",
+              "operation": "create"
+            },
+            "health": "ok",
+            "evaluationTime": 0.000214,
+            "lastEvaluation": "2024-04-29T14:23:53.403557247+02:00",
+            "type": "recording"
+          },
+          {
+            "name": "metric2",
+            "query": "0",
+            "labels": {
+              "namespace": "ns1",
+              "operation": "update"
+            },
+            "health": "ok",
+            "evaluationTime": 0.000214,
+            "lastEvaluation": "2024-04-29T14:23:54.403557247+02:00",
+            "type": "recording"
+          },
+          {
+            "name": "metric2",
+            "query": "0",
+            "labels": {
+              "namespace": "ns1",
+              "operation": "delete"
+            },
+            "health": "ok",
+            "evaluationTime": 0.000214,
+            "lastEvaluation": "2024-04-29T14:23:53.603557247+02:00",
+            "type": "recording"
+          },
+          {
+            "state": "firing",
+            "name": "Alert1",
+            "query": "metric1{namespace=\"ns1\"} == 0",
+            "duration": 0,
+            "keepFiringFor": 0,
+            "labels": {
+              "namespace": "ns1"
+            },
+            "annotations": {},
+            "alerts": [
+              {
+                "labels": {
+                  "alertname": "Alert1",
+                  "namespace": "ns1"
+                },
+                "annotations": {},
+                "state": "firing",
+                "activeAt": "2019-12-18T13:14:44.543981127+01:00",
+                "value": "0e+00"
+              }
+            ],
+            "health": "ok",
+            "evaluationTime": 0.000214,
+            "lastEvaluation": "2024-04-29T14:23:53.803557247+02:00",
+            "type": "alerting"
+          },
+          {
+            "state": "firing",
+            "name": "Alert2",
+            "query": "metric2{namespace=\"ns1\"} == 0",
+            "duration": 0,
+            "keepFiringFor": 0,
+            "labels": {
+              "namespace": "ns1"
+            },
+            "annotations": {},
+            "alerts": [
+              {
+                "labels": {
+                  "alertname": "Alert2",
+                  "namespace": "ns1",
+                  "operation": "update"
+                },
+                "annotations": {},
+                "state": "firing",
+                "activeAt": "2019-12-18T13:14:44.543981127+01:00",
+                "value": "0e+00"
+              },
+              {
+                "labels": {
+                  "alertname": "Alert2",
+                  "namespace": "ns1",
+                  "operation": "delete"
+                },
+                "annotations": {},
+                "state": "firing",
+                "activeAt": "2019-12-18T13:14:44.543981127+01:00",
+                "value": "0e+00"
+              }
+            ],
+            "health": "ok",
+            "evaluationTime": 0.000214,
+            "lastEvaluation": "2024-04-29T14:23:53.903557247+02:00",
+            "type": "alerting"
+          }
+        ],
+        "interval": 10
+      }
+    ]
+  }
+}
\ No newline at end of file