diff --git a/cmd/karma/main.go b/cmd/karma/main.go
index d7e23c980..a1b3305d8 100644
--- a/cmd/karma/main.go
+++ b/cmd/karma/main.go
@@ -56,8 +56,13 @@ var (
 )
 
 func getViewURL(sub string) string {
-	u := path.Join(config.Config.Listen.Prefix, sub)
-	if strings.HasSuffix(sub, "/") && !strings.HasSuffix(u, "/") {
+	var fixedSub string
+	fixedSub = sub
+	if !strings.HasPrefix(sub, "/") {
+		fixedSub = "/" + sub
+	}
+	u := path.Join(config.Config.Listen.Prefix, fixedSub)
+	if strings.HasSuffix(fixedSub, "/") && !strings.HasSuffix(u, "/") {
 		// if sub path had trailing slash then add it here, since path.Join will
 		// skip it
 		return u + "/"
diff --git a/cmd/karma/tests/testscript/invalid_listen_prefix.txt b/cmd/karma/tests/testscript/invalid_listen_prefix.txt
new file mode 100644
index 000000000..d1b1a46a3
--- /dev/null
+++ b/cmd/karma/tests/testscript/invalid_listen_prefix.txt
@@ -0,0 +1,4 @@
+# Raises an error if listen.prefix is invalid
+karma.bin-should-fail --log.format=text --log.config=false --log.level=error --alertmanager.uri http://localhost --listen.prefix karma
+! stdout .
+stderr 'msg="listen.prefix must start with ''\/'', got \\"karma\\"'
diff --git a/internal/alertmanager/model_test.go b/internal/alertmanager/model_test.go
index 5ccff879f..13b68528a 100644
--- a/internal/alertmanager/model_test.go
+++ b/internal/alertmanager/model_test.go
@@ -1,7 +1,11 @@
 package alertmanager
 
 import (
+	"fmt"
 	"testing"
+
+	"github.com/prymitive/karma/internal/config"
+	log "github.com/sirupsen/logrus"
 )
 
 type uriTest struct {
@@ -101,3 +105,91 @@ func TestAlertmanagerURI(t *testing.T) {
 		}
 	}
 }
+
+func TestAlertmanagerSilenceByID(t *testing.T) {
+	am, err := NewAlertmanager("cluster", "test", "http://localhost")
+	if err != nil {
+		t.Error(err)
+	}
+
+	_, err = am.SilenceByID("foo")
+	if err == nil {
+		t.Error("am.SilenceByID(foo) didn't return any error")
+	}
+}
+
+func TestAlertmanagerInternalURI(t *testing.T) {
+	type testCaseT struct {
+		prefix string
+		proxy  bool
+		uri    string
+	}
+	tests := []testCaseT{
+		{
+			prefix: "/",
+			proxy:  false,
+			uri:    "http://localhost",
+		},
+		{
+			prefix: "/",
+			proxy:  true,
+			uri:    "/proxy/alertmanager/default",
+		},
+		{
+			prefix: "/root",
+			proxy:  true,
+			uri:    "/root/proxy/alertmanager/default",
+		},
+		{
+			prefix: "/root/",
+			proxy:  true,
+			uri:    "/root/proxy/alertmanager/default",
+		},
+		{
+			prefix: "root",
+			proxy:  true,
+			uri:    "/root/proxy/alertmanager/default",
+		},
+		{
+			prefix: "root/",
+			proxy:  true,
+			uri:    "/root/proxy/alertmanager/default",
+		},
+	}
+
+	for _, testCase := range tests {
+		t.Run(fmt.Sprintf("prefix=%q proxy=%v uri=%q", testCase.prefix, testCase.proxy, testCase.uri), func(t *testing.T) {
+			config.Config.Listen.Prefix = testCase.prefix
+			am, err := NewAlertmanager("cluster", "default", "http://localhost", WithProxy(testCase.proxy))
+			if err != nil {
+				t.Error(err)
+			}
+
+			uri := am.InternalURI()
+			if uri != testCase.uri {
+				t.Errorf("am.InternalURI() returned %q, expected %q", uri, testCase.uri)
+			}
+		})
+	}
+}
+
+func TestAlertmanagerSanitizedURI(t *testing.T) {
+	am, err := NewAlertmanager("cluster", "test", "http://user:pass@localhost")
+	if err != nil {
+		t.Error(err)
+	}
+
+	uri := am.SanitizedURI()
+	if uri != "http://user:xxx@localhost" {
+		t.Errorf("am.SanitizedURI(http://user:pass@localhost) returned %q", uri)
+	}
+}
+
+func TestAlertmanagerPullWithInvalidURI(t *testing.T) {
+	log.SetLevel(log.PanicLevel)
+	am, _ := NewAlertmanager("cluster", "test", "%gh&%ij")
+	err := am.Pull()
+	if err == nil {
+		t.Error("am.Pull(invalid uri) didn't return any error")
+	}
+}
diff --git a/internal/alertmanager/models.go b/internal/alertmanager/models.go
index 508c7b62d..816dc6668 100644
--- a/internal/alertmanager/models.go
+++ b/internal/alertmanager/models.go
@@ -3,6 +3,7 @@ package alertmanager
 import (
 	"fmt"
 	"net/http"
+	"net/url"
 	"path"
 	"sort"
 	"strings"
@@ -159,14 +160,10 @@ func (am *Alertmanager) pullSilences(version string) error {
 func (am *Alertmanager) InternalURI() string {
 	if am.ProxyRequests {
 		sub := fmt.Sprintf("/proxy/alertmanager/%s", am.Name)
-		uri := path.Join(config.Config.Listen.Prefix, sub)
-		if strings.HasSuffix(sub, "/") {
-			// if sub path had trailing slash then add it here, since path.Join will
-			// skip it
-			return uri + "/"
+		if strings.HasPrefix(config.Config.Listen.Prefix, "/") {
+			return path.Join(config.Config.Listen.Prefix, sub)
 		}
-
-		return uri
+		return path.Join("/"+config.Config.Listen.Prefix, sub)
 	}
 
 	// strip all user/pass information, fetch() doesn't support it anyway
@@ -311,6 +308,12 @@ func (am *Alertmanager) Pull() error {
 
 	version := am.probeVersion()
 
+	// verify that URI is correct
+	_, err := url.Parse(am.URI)
+	if err != nil {
+		return err
+	}
+
 	status, err := am.fetchStatus(version)
 	if err != nil {
 		am.clearData()