diff --git a/.changelog/14034.txt b/.changelog/14034.txt
new file mode 100644
index 0000000000..216c5406a3
--- /dev/null
+++ b/.changelog/14034.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+cli: When launching a sidecar proxy with `consul connect envoy` or `consul connect proxy`, the `-sidecar-for` service ID argument is now treated as case-insensitive.
+```
diff --git a/command/connect/proxy/proxy.go b/command/connect/proxy/proxy.go
index d2d0b90cf1..a0477a6a10 100644
--- a/command/connect/proxy/proxy.go
+++ b/command/connect/proxy/proxy.go
@@ -232,7 +232,7 @@ func LookupProxyIDForSidecar(client *api.Client, sidecarFor string) (string, err
 	var proxyIDs []string
 	for _, svc := range svcs {
 		if svc.Kind == api.ServiceKindConnectProxy && svc.Proxy != nil &&
-			strings.ToLower(svc.Proxy.DestinationServiceID) == sidecarFor {
+			strings.EqualFold(svc.Proxy.DestinationServiceID, sidecarFor) {
 			proxyIDs = append(proxyIDs, svc.ID)
 		}
 	}
diff --git a/command/connect/proxy/proxy_test.go b/command/connect/proxy/proxy_test.go
index ae7b1cdfbc..28d5a9da21 100644
--- a/command/connect/proxy/proxy_test.go
+++ b/command/connect/proxy/proxy_test.go
@@ -110,6 +110,17 @@ func TestCommandConfigWatcher(t *testing.T) {
 				require.Equal(t, 9999, cfg.PublicListener.BindPort)
 			},
 		},
+
+		{
+			Name: "-sidecar-for, one sidecar case-insensitive",
+			Flags: []string{
+				"-sidecar-for", "One-SideCar",
+			},
+			Test: func(t *testing.T, cfg *proxy.Config) {
+				// Sanity check we got the right instance.
+				require.Equal(t, 9999, cfg.PublicListener.BindPort)
+			},
+		},
 	}
 
 	for _, tc := range cases {